WO2000054359A1

WO2000054359A1 - Dual battery systems and methods for maintaining the charge state of high power batteries

Info

Publication number: WO2000054359A1
Application number: PCT/US2000/006558
Authority: WO
Inventors: Arnold Allen; James Spencer; Victor Rompa
Original assignee: Bolder Technologies Corporation
Priority date: 1999-03-11
Filing date: 2000-03-13
Publication date: 2000-09-14
Also published as: AU3527500A

Abstract

The invention provides dual battery assemblies and methods for maintaining the charge state of a high power battery. In certain embodiments, the assembly provides a unified system where the second battery (40) can recharge the first battery (10) after deep discharge. The assemblies are useful in providing current for applications which require a high amount of current over a short period and for providing current to other applications which require low levels of current for extended periods. The present invention also provides a dual battery assembly which utilizes a second battery (40) and current control components to maintain the functionality of the first battery (10) for significantly longer periods than if the first battery was allowed to undergo the process of self discharge. The presented apparatus and methods can achieve these results using cost-effective, readily-available secondary batteries and do not require user maintenance or a corded source of electricity.

Description

DUAL BATTERY SYSTEMS AND METHODS FOR MAINTAINING THE CHARGE STATE OF HIGH POWER BATTERIES

FIELD OF INVENTION The present invention relates to the field of batteries, including those which can be used as portable power supplies. More specifically, in one embodiment, the present invention relates to the field of dual battery systems in which the state of charge of a first battery is maintained by a second battery, especially during periods when the first battery sits idle. In another embodiment, the present invention relates to a dual battery system in which the first battery is capable of very high discharge rates, whereas the second battery has sufficient capacity so that it can provide lower levels of current for extended periods and also recharge the first battery after periods of deep discharge.

BACKGROUND OF INVENTION One problem frequently encountered with batteries of all types is the loss of charge during periods in which the battery is not used; this can be a particular problem with certain high power batteries. The extent to which loss of charge over time is problematic is a function of the chemical reactions within the cell and the physical design of the battery, especially the electrodes. A second problem involves recharging a battery after periods of deep discharge and/or providing a single power source which is capable of satisfying the various current demands for differing applications.

Because lead-acid batteries remain a predominant device for delivering electrical current in many electrical operations, the problems just described have particular import as related to such batteries. Lead-acid batteries retain their popularity as an electrical energy source because they can be manufactured easily and relatively inexpensively, are rechargeable and are capable of delivering relatively high power. They also can withstand rugged treatment and can be stored for extended periods.

There are two major classes of lead-acid batteries. Conventional lead-acid batteries such as valve-regulated lead-acid batteries are typically comprised of a plurality of cells. Each cell typically includes a set of interleaved monopolar positive and negative electrodes or plates which are separated by a porous separator. The electrodes or plates are typically composed of a lead or lead alloy current collector and an electrochemically active paste which is coated onto the exterior surfaces of the current collector. In conventional lead-acid batteries, the current collectors are in the form of a grid and are relatively thick. In newer improved lead-acid batteries, the current collectors are made of ultra-thin films or foils (lead or lead alloys) which are wound into a "jelly roll" configuration. The development of such batteries has been pioneered by the assignee of the current invention and the particular design features of such batteries are described in U.S. Patent 5,047,300, U.S. Patent 5,045,086 and U.S. Patent 5,368,961. Batteries utilizing such thin plate design are referred to by the assignee of the current invention as

"Thin Metal Foil" batteries, or simply "TMF" batteries. Lead-acid batteries of this design are capable of very high discharge and recharge rates. The thin plate design means that such batteries are also significantly lighter and smaller than their conventional counterparts. Like other batteries, lead-acid batteries, including those of the TMF design, are susceptible to losing charge during periods in which they sit idle. Loss of charge over time is affected by a process called "self-discharge" - chemical reactions within the battery which cause the consumption of electrolyte, even when the battery is not exposed to an external load. The consumption of electrolyte through self-discharge decreases discharge capacity because the discharge capacity of a battery is proportional to the specific gravity, or concentration, of electrolyte within the battery. Thus, self-discharge reduces the shelf life of the battery (i.e., the period of time during which the battery maintains sufficient discharge capacity for its intended purpose when the battery is allowed to sit idle without having to provide current to an external load), but it also results in voltage decay (i.e.. a decrease in open circuit voltage).

As indicated above, the ability of a battery to retain charge while sitting idle is dependent in large measure on the chemistry within the battery, especially the chemical reactions that occur at the interface between the current collector and the paste. With certain current collectors, especially pure lead and low-tin alloy current collectors, a passivation layer can form at this interface. The passivation layer reduces the process of self-discharge but negatively impacts cycle life (the number of discharging and recharging cycles a battery can sustain while still delivering a certain level of electricity). Other current collectors, such as those containing higher levels of tin for instance, form a conductive or semi-conducting layer at the current collector/paste interface. While such batteries have good cycle life, the improved cycle life comes at the cost of a decrease in shelf life.

Thus, one approach for dealing with the loss of battery charge during periods of non-use has been to vary the composition of the current collectors in an effort to optimize both shelf life and cycle life. As alluded to above, however, increases in shelf life typically occur at the expense of cycle life. Other approaches have included instructing the user of the battery to recharge the battery at regular and frequent intervals. This approach is not convenient and also generally requires a corded power source to recharge the battery. Consequently, there remains a need for an apparatus and methods which can maintain high power battery functionality for long periods of time without requiring user maintenance and a corded power supply.

It is also desirable to have a dual battery assembly using lead-acid batteries wherein one battery can recharge the other after periods of deep discharge and wherein the two batteries have different discharge capabilities to meet the differing current requirements of various applications. In dual battery assemblies designed to meet this specific need, the first battery generally has a high discharge rate but relatively low capacity; the second battery has a low discharge rate but high capacity. For instance, a dual battery assembly of the design just described would be useful in recharging a battery that was drained during periods of extended use without recharging or otherwise weakened (e.g., a battery drained when car lights are inadvertently left on or a battery whose performance is reduced because of the cold). In such a case, the first battery with its high discharge rate can be used to "jump" the depleted battery; the second battery with its lower discharge rate and higher capacity can be used to recharge the first battery. A dual battery assembly of this type is also useful because the first battery can provide high levels of current within a short time period for applications requiring such current, whereas the second battery can be used to deliver current to devices requiring low levels of current for extended time periods (e g , personal entertainment dev ices such as radios and televisions)

Several different dual battery systems have been descπbed including U S Patent 5,223,351 to Wruck, U S Patent 2,616,937 to Kullgren, U S Patent 5,614,331 to Takeuchi et al , U S Patent 5,565,756 to Urbish et al , U S Patent 4,770,954 to

Noordenbos, U S Patent 5,194,799 to Tomantschger, U S Patent 3,165,689 to Hughes, 5,352,966 to Irons, U S Patent 3,883,368 to Kordesch et al , European Patent 370534 Bl to Witehira, German Patent 1005142, Canadian Patent 2,171,603 to Maston, et al , abstract of Japanese patent J06078465, abstract of Japanese patent J03210775, PCT publication WO98/40926, European application 513531 Al, and German application

1961 1776 Al However, none of these dual battery systems are believed to include all the features of the dual batteries of the present designs descπbed herein, especially those designs wherein inexpensive batteπes are used to maintain the state of charge of high powered batteπes

SUMMARY OF INVENTION

The present invention satisfies the needs identified above by providing dual battery systems of varying design but which generally include a first battery that is connected in parallel to a second battery In certain embodiments, the second battery can recharge the first battery after discharge of the first battery The second battery can also be used to provide current for those applications which require low levels of current over extended peπods, while the first battery can be used in situations in which a high level of current must be generated over a short time peπod In other embodiments, the second battery is connected in a circuit so that it supplies a low-level current that maintains the charge of the first battery that otherwise would undergo a relatively rapid loss of charge over time due to the process of self-discharge Various embodiments are particularly useful as portable power supplies which can be used to jump start cars and/or power various personal devices which require lower levels of current

More particularly, in embodiments wherein the dual battery system is capable of providing two levels of current, the system includes (l) a first battery, (a) a second battery, and (in) a circuit connecting the first and second battery in parallel In general, the first battery in such embodiments has a relatively high power density as compared to the second battery, whereas the second battery has a higher energy density (1 e , capacity) than the first battery Thus, the first battery is selected so as to have a first peak amperage which exceeds the second peak amperage of the second battery The first battery also has a faster discharge rate than that of the second battery The first battery may also have a self-discharge rate which is greater than the corresponding rate for the second battery Finally, the second battery is also typically of lower cost than the first battery

In another aspect, the present invention provides dual battery systems having the same general design of that just descπbed but with additional components to control current flow through the assembly More specifically these embodiments include the necessary elements to restπct current so that it only flows from the second battery to the first battery, the current may be further restπcted so that it is sufficient to maintain the charge of the first battery duπng peπods of non-use, but insufficient to provide current to an external load Embodiments of this general design compπse (I) a first battery having a first energy density (capacity) and (n) a second battery having a second energy density which is greater than the first energy density of the first battery, (in) an electπcal circuit which connects the first and second battery in parallel and (iv a current direction regulator connected to the circuit which functions to prevent current from passing from the first battery to the second battery Typically, the current direction regulator is a diode, although other circuitry or devices which limit current flow in the desired manner could be used as well In this manner, it is possible to maintain the state of charge of the first battery without user intervention for significantly longer peπods than if the first battery was simply left alone The dual battery system in these embodiments may also include a current level controller which limits the function of the second battery to only passing a very low level of current for the maintenance of the state of charge of the first battery The current level controller may be a resistor but other circuitry or devices restπcting the amount of current flow from the second battery to the first battery could be utilized instead Thus, in contrast to the embodiments which do not include the current direction regulator and current level controller, the second battery in this alternative embodiment is prevented from participating in the functional capability of the first battery, i.e., the current level controller prevents the second battery from passing current to an external load. The first battery and second battery in these embodiments have the same characteristics as the first and second batteπes discussed above in those embodiments which lack the current control elements. Additionally, because the current direction regulator prevents current from flowing from the first battery to the second battery, it is possible for the open circuit voltage (OCV) of the second battery to initially be less than that for the first battery. This contrasts with the typical situation in which the OCV of the second battery exceeds the OCV of the first battery. Dual battery assemblies using first batteries having a higher OCV can be used, for instance, when the self-discharge rate of the first battery is sufficiently faster than that of the second battery so that at some point after the two batteries are connected the OCV voltage of the second battery exceeds that of the first battery. This type of arrangement could also be utilized if the voltage of the first battery decreased more rapidly with discharge than the second battery.

Dual battery systems which incorporate the current control elements provide several advantages. First, dual battery assemblies of these designs provide a cost effective way to extend the fundamental charge retention characteristics of a high power battery. Using the dual battery system of these designs, it is possible to increase the charge retention of high power batteπes by at least two times or more. In fact, by replacing the second battery, it is possible to extend the functional life of the first battery almost indefinitely. Furthermore, the dual battery systems provided by the present invention alleviates the need to frequently recharge the first battery and avoids having to use corded electπcal sources to recharge the first battery. Regardless of the particular embodiment, the first battery can be of a vaπety of types but most preferably is a lead-acid battery, a nickel cadmium battery or a nickel hydπde battery, although batteπes of different chemistries could also be used. The first battery is preferably a lead-acid battery, especially one utilizing ultra-thin current collectors or plates. The negative current collector, and preferably the positive current collector as well, are preferably 0 005 inches or less thick. It is also preferred that at least the positive current collector, and optionally the negative current collector, be a substantially non-perforated foil. The positive and negative current collectors may be coated on their two major faces with paste to yield a plate; these plates are preferably 0.010 inches thick or less. Batteries using such ultra-thin plates and/or current collectors are referred to as Thin Metal Foil cells, or simply TMF cells.

The second battery in the different embodiments can include a variety of different battery types, including, but not limited to, a lead-acid battery or an alkaline battery. If the second battery is a lead-acid battery, it preferably is of a conventional design wherein the current collectors are lead or lead alloy grids. In certain preferred embodiments, however, the second battery is an alkaline cell or collection of alkaline cells. The use of alkaline batteries is advantageous because of their low cost and because they are energy dense.

In an especially preferred embodiment, the dual battery assemblies described herein include an alkaline cell or cells as the second battery and a TMF cell or cells as the first battery. The combination of these batteries when connected in parallel produces an assembly in which the unique power capabilities of the TMF battery can be made available on demand over a long period of time without any external maintenance by the user of the dual battery assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial view of a dual battery assembly according to a preferred embodiment of the present invention.

FIG. 2 is a pictorial view of a dual battery assembly according to another preferred embodiment of the present invention wherein a diode and resistor are included within the circuit that connects the batteries in order to control current flow between the two batteries.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides two major embodiments of a dual battery system, each designed to solve particular problems associated with battery power supplies. The first ma_jor embodiment is useful for providing a unified system wherein a first battery can be recharged by a second battery after the first battery has been subjected to deep discharge Assemblies of this first type are also useful in providing current for applications which require a high amount of current over a short peπod of time (first battery function) and for providing current to other applications which only require low levels of current but for extended peπods of time (second battery function)

In a vaπation on the design just descπbed, the present invention further provides a dual battery assembly which utilizes a second battery and vaπous current control components to maintain the functionality of the first battery for significantly longer peπods of time than if the first battery was simply allowed to undergo the normal process of self-discharge The apparatus and methods of the present invention can achieve these results using cost effecti e and readily available second batteries and do not require user maintenance or a corded source of electπcity In both of these major embodiments, the term "battery" as used herein is meant to include assemblies containing a single cell or a collection of cells

With reference now to FIG 1, one general design for the apparatus of the present invention is depicted The dual battery assembly generally includes a first battery 10 and a second battery 40 The first battery 10 includes a positive terminal 12 and a negative terminal 14 Likewise, the second battery 40 includes a positive terminal 20 and a negative terminal 18 The first battery 10 and second battery 40 are connected at their respective terminals by connector 16 and connector 26 to form a circuit, wherein the first battery 10 and second battery 40 are connected in parallel External loads can be attached at terminals 15 and 25

The second battery 40 can be enclosed in a housing 30 in order to provide a convenient means for handling the cell or cells that compπse the second battery 40

Similarly, the cell or cells that make up the first battery 10 can be placed within a housing (not shown) to facilitate ease in handling It is also possible to include both the first battery 10 and the second battery 40 within a single housing The positive and negative terminals of the first battery 10 and second battery 40 may be connected to positive and negative terminals, respectively, positioned on the exteπor of a case which is designed to hold both batteπes

In certain embodiments of the general design depicted in FIG 1 , the first battery 10 has a first peak amperage and the second battery 40 has a second peak amperage, wherein the peak amperage of the first battery 10 exceeds that of the second battery 40, particularly with respect to size and weight Preferably, the first battery 10 and the second battery 40 are capable of being recharged It is preferred that the peak amperage of the first battery 10 be sufficient to start an automobile engine by itself, or in combination with the second battery 40 Ideally, the first battery 10 is capable of dehveπng sufficient power to start a car engine several times before needing to be recharged In contrast, the second battery 40 is characteπzed by having a higher energy density (l e , higher capacity) than the first battery 10 The capacity of the second battery 40 is such that the second battery 40 can deliver relatively low levels of current at many different times without requiπng recharging between uses Thus, the first battery 10 is charactenzed as having a high power density, while the second battery 40 is characteπzed by having a high energy density

In certain embodiments, the first battery 10 also has a first open circuit voltage (OCV), and the second battery 40 has a second OCV which is greater than the OCV of the first battery 10 of the second battery 40 A design of this type results in a low-level current which flows from the second battery 40 to the first battery 10, thereby maintaining the state of charge of the first battery 10 that would otherwise be lost through the normal self-discharge reactions that are associated with the first battery 10 In another aspect, the self-discharge rate of the first battery 10 is greater than the corresponding rate for the second battery 40 This means that the shelf-life of the second battery 40 is longer than the shelf-life of the first battery 10 (shelf-life referπng to the time duπng which the battery maintains sufficient discharge capability for its intended purpose when the battery is allowed to sit without use)

In addition to these characteπstics, in the general embodiment shown in FIG 1, the first battery 10 and the second battery 40 are selected so that the second battery 40 has the necessary capacity to recharge the first battery 10 after the first battery has been discharged. In general this means that the nominal voltage of the two batteries are roughly equivalent; furthermore, the voltage of the second battery 40 preferably does not decrease as rapidly with discharge as compared to the voltage decrease associated with discharge of the first battery 40. Thus, after the dual battery system is used, the voltage of the second battery is sufficiently greater than the voltage of the first battery so that the second battery can recharge the first battery.

Although the first battery in FIG. 1 is shown as being comprised of 6 individual cells, it should be appreciated that the exact number of cells is not critical to the present invention. The number of cells can be varied according to the particular performance characteristics that are desired for each application. Likewise, the manner in which the individual cells comprising the first battery 10 are interconnected is not a critical aspect of the invention. For instance, the cells can be connected in series or in a parallel configuration depending upon the specific performance criteria which are required. The same is true for the second battery 40. While FIG. 1 depicts 9 individual cells as comprising the second battery 40, here too, it should be understood that the exact number of cells and the connections there between can be varied according to the particular demands of the application for which the dual battery assembly is to be used.

The first battery 10 can be any of a number of different battery chemistries so long as the cπteria set forth above are satisfied. For instance, the first battery may be a lead-acid battery, a nickel cadmium battery or a nickel hydride battery. In particularly preferred embodiments, the first battery 10 of the present invention includes lead-acid batteries such as those described in U.S. Patent 5,047,300 to Juergens, U.S. Patent 5,045,086 to Juergens and U.S. Patent 5,368,961 to Juergens; these patents are assigned to the assignee of the present invention and are incorporated by reference herein. Batteries of these designs are characterized by having ultra-thin current collectors and pasted current collectors or plates. The plates or foils in such batteries are spirally wound. Batteries having the characteristics described in these patents are referred to by the assignee of the current invention and referred to herein as being TMF (Thin Metal Foil) cells or batteries. Briefly, batteries of the TMF design include ultra-thin current collectors and plates. The negative current collector, and optionally the positive current collector, in TMF cells typically are 0.005 inches thick or less. It is also preferred that the positive current collectors, and preferably the negative current collectors as well, are substantially non-perforated. The term "substantially non-perforated" is defined herein to mean that the foil is essentially a solid film of metal rather than existing as a grid which is the traditional form for current collectors used in lead-acid batteries. The term allows for the possibility, however, that the foil or film may include a very limited number of small holes therein. Given their shape as ultra-thin foils, the positive and negative current collectors each have two major faces which can be coated with a layer of paste. The combination of the current collectors and layers of paste are referred to as "plates" within the industry. The paste thickness of each layer applied to the current collectors is 0.005 inches or less thick and preferably 0.002 to 0.003 inches thick. Thus, the negative plates, and optionally the positive plates, are typically 0.010 inches thick or less. In certain embodiments, however, the foil and plates may be thicker. For example, in some embodiments the foil may be 0.008 inches or less thick and the plate may be 0.015 inches or less thick.

Preferably, the positive and negative current collectors or plates in the battery are cast on to positive and negative end connectors which separately join the positive and negative current collectors or plates. Details of the end connector design can be found by reference to U.S. Patent 5,198,313 to Juergens, which is assigned to the assignee of the present invention and is incorporated herein by reference.

The second battery 40 can be selected from batteries which have the characteristics set forth above. In certain embodiments, the second battery may include conventional lead-acid batteries which utilize current collectors of the standard grid design which are also thicker than those found in the TMF design.

Plates in conventional lead-acid batteries are formed by forcing paste into the interstices of the grid. The plates are thicker than those of the TMF design; the plates may be 0.05 inches thick or greater for example. Although conventional lead-acid batteries cannot achieve the discharge rate of TMF batteries, they have the advantage of being able to store more capacity in a smaller size and with less eight and cost as compared to the TMF batteπes.

Conventional lead-acid batteπes are one preferred type of battery for the second battery because of their low cost relative to TMF batteries. In other preferred embodiments, however, the second battery 40 is an alkaline cell, such as a zinc manganese dioxide cell that is available from any of the major commercial battery manufacturers. The use of alkaline cells in the second battery 40 is preferred because of their low cost, high energy density and low self-discharge characteristics. It would also be possible to use a nickel cadmium, lithium or metal hydride battery. Because the second battery 40 preferably has a high energy density, it is not necessary to store all the required capacity in the first battery 10. The dual battery assembly of the design descπbed may undergo significant idle periods between use. Duπng these idle peπods, energy is transferred from the second battery 40 to the first battery 10, thereby putting the first battery 10 at full charge for subsequent applications. Thus, in general, increased capacity in the second battery 40 is desirable; the capacity of the second battery 40 should be greater than that of the first battery 10. For example, the capacity of the second battery 10 may be approximately 10 times that of the first battery 10; however, other capacity ratios can be used.

In certain embodiments, both the first and second batteπes 10, 40 may be lead- acid batteπes, with the distinction being that the first battery 10 is of the TMF design while the second battery 40 is of conventional design. Other embodiments, however, may involve combinations of different battery types When utilizing batteπes of diffeπng electrochemistries, it is important for proper functioning of the assembly that the batteries have essentially the same nominal voltage. Those skilled in the art will recognize that by correctly connecting individual cells in parallel or seπes, varying different nominal voltages can be obtained as desired

In a particularly preferred embodiment, the dual battery assembly comprises a first battery 10 that is of the TMF design and a second battery 40 that is an alkaline battery. These embodiments are particularly useful because the combination of the TMF battery and alkaline battery yields a dual battery assembly in which the high power and rapid discharge characteπstics of the TMF batter, can be made av ailable for extended time peπods without any external maintenance by the user of the assembly These embodiments in which the first battery 10 is a TMF battery and the second battery 40 is a conventional lead-acid battery or seπes of alkaline batteπes are particularly useful as portable power supplies because such combinations can generate very high peak amperages and high discharge rates (first battery) while still having high capacity (second battery), all in a combination which is relatively inexpensive and modest in weight and

An alternative embodiment is illustrated in FIG 2 The dual battery assembly of this design is quite similar to that shown in FIG 1 The assembly differs in that the circuit connecting the two batteπes includes a current direction regulator 22 and may also include a current level controller 24 to control the direction and amount of current flow between the two batteπes 10, 40 Assemblies having the design depicted in FIG 2 are designed to maintain the charge of the first battery duπng extended peπods of non-use As with the embodiment depicted in FIG 1, the dual battery assembly shown in

FIG 2 generally includes a first battery 10 and a second battery 40 The first battery 10 includes a positive terminal 12 and a negative terminal 14 Likewise, the second battery 40 includes a positive terminal 20 and a negative terminal 18 The first battery 10 and second battery 40 are connected at their respective terminals by connector 16 and connector 26 to form a circuit, wherein the first battery 10 and second battery 40 are connected in parallel An external load can be connected at terminals 15, 25

This general embodiment also includes a current direction regulator 22 within the circuit that connects the first battery 10 and the second battery 40 As depicted in FIG 2, the current direction regulator 22 can be connected in seπes between the positive terminals 20, 12 of the second and first batteπes 40, 10, respectively The current direction regulator 22 prevents current from flowing from the first battery 10 to the second battery 40, instead, the current direction regulator 22 keeps current only flowing from the second battery 40 to the first battery 10 When the current direction regulator 22 functions in this manner, the state of charge of the first battery 10 can be maintained without user intervention for substantially longer penods than if the first battery 10 was functioning independently As shown in FIG 2, the current direction regulator can be a diode. However, the current direction regulator could be other devices, circuitry or means which restπct current so that it only flows from the second battery 40 to the first battery 10. A current level controller 24 can also be included within the circuit that joins the first battery 10 and the second battery 40 as further shown in FIG. 2 The current level controller 24 can be connected in seπes within the circuit between the positive terminal 20 of the second battery 40 and the positive terminal 12 of the first battery 10 Preferably, the current level controller 24 is used in conjunction with the current direction regulator 22 and is positioned within the circuit between the current direction regulator 22 and the positive terminal 12 of the first battery 10 The current level controller 24 limits the amount of current that can pass from the second battery 40 to the first battery 10 More specifically, the current level controller 24 preferably restπcts current flow from the second battery 40 to the first battery 10 to a level which is sufficient to maintain the charge of the first battery 10 but insufficient to participate in the functional capability of the first battery 10 (l e , the second battery does not produce current for an external load). Said differently, the current level controller 24 acts to ensure that the first battery 10 operates within its rated capabilities without any current discharge contπbution from the second battery 40 Thus, dual battery assemblies of the design shown in FIG. 2 function somewhat differently than the assembly shown in FIG 1 in that the second battery 40 does not deliver current to an external load

The current level controller 24 can be a resistor as shown in FIG. 2 However, other circuitry, devices or means which similarly restπct the level of current flowing to the first battery 10 can be utilized as well The general characteπstics of the first battery 10 and the second battery 40 are generally the same as those descπbed above in the descπption of the embodiment shown in FIG. 1 As indicated above, the OCV of the second cell typically is greater than the OCV of the second cell, this results in a low-level of current flowing from the second battery 40 to the first battery 10 to maintain the state of charge of the first battery 10. However, in certain embodiments of the type shown in FIG. 2, the OCV of the first battery 10 may initially exceed the OCV of the second battery 40. The current direction regulator 22 in these instances ensures that current still does not flow from the first battery 10 to the second battery 40. In such cases, the voltage of the first battery 10 must drop below that of the second battery 40 before the second battery 40 can recharge the first battery 10. This could occur, for example, when the self-discharge rate of the first battery 10 is sufficiently faster than that of the second battery 40 so that at some point after the batteries are connected the OCV of the second battery 40 is greater than that of the first battery 10. An arrangement of this type would also work in those cases wherein the voltage of the first battery 10 decreased more rapidly with discharge as compared to the second battery 40.

As to chemical type, the first battery, can include any of the types described in relation to FIG. 1 , including for instance a lead-acid, nickel cadmium or nickel metal hydride battery. Preferably, the first battery 40 is a lead-acid battery, and more preferably is of the TMF design. The second battery 40 may be a conventional lead-acid battery, or more preferably is an alkaline battery because of their small size and low cost. In particularly preferred embodiments, the first battery 10 is a lead-acid battery, especially one of the TMF design and the second battery 40 is an alkaline battery.

Using a system in which the first battery 10 is of the TMF design and the second battery 40 includes a series of alkaline cells such as can be bought from any commercial supplier, it is possible to extend the shelf-life of the first battery 40 by at least a factor of

2. Of course, if the inexpensive alkaline cells are replaced, it is possible to maintain the shelf-life, and thus access to the high power performance of the TMF first battery, essentially indefinitely.

The present invention also provides methods for maintaining the charge state of high power batteries. The methods generally comprise connecting a first battery 10, a second battery 40, and a current direction regulator 22 to form an electrical circuit wherein the first battery 10 and the second battery 40 are connected in parallel; the current direction regulator is connected in series between the first and second battery 10, 40. The method can further include connecting a current level controller 24 into the circuit in order to restrict the amount of current flow from the second battery 40 to the first battery 10. The current level controller is connected in series with the first and second battery 10, 40. The current level controller 24 acts to limit current flow from the second battery 40 to a level which maintains the charge on the first battery but which is insufficient to provide current to an external load.

As discussed above, current direction regulator 22 may be a diode or other means which prevents current flow from the first battery 10 to the second battery 40. The current level controller 24 can be a resistor or similar means for achieving the same effect.

The particular type of first battery 10 and second battery 40 is not particularly critical so long as the batteries have the characteristics described above in relation to FIGS. 1 and 2. The methods preferably include connecting a first battery 10 such as a lead-acid, a nickel cadmium or a nickel hydride cell with a second battery 40 which is preferably a lead-acid battery of conventional design or an alkaline battery. Most preferably, a lead-acid battery of the TMF design is connected with an alkaline battery. All of the references listed herein are incorporated herein by reference.

Claims

We claim

1 A dual battery system, compnsing

(a) a first battery, said first battery being rechargeable and having a first energy density, (b) a second battery having a second energy density which is greater than said first energy density,

(c) an electπcal circuit connecting said first and second battery in parallel, and

(d) a current direction regulator electπcally connected to said circuit to prevent current flow from said first battery to said second battery

2 A dual battery system according to claim 1, wherein said current direction regulator is a diode connected in series with said first battery and said second battery

3 A dual battery system according to claim 1, further includmg a current level controller within said circuit which restπcts the amount of current that can pass from said second battery to said first battery

4 A dual battery system according to claim 3, wherein said current level controller is a resistor connected in seπes with said first battery and said second battery

5 A dual battery system according to claim 4, wherein said resistor restπcts current flow from said second battery to said first battery to a desired low level which is sufficient to maintain the charge of said first battery but insufficient to participate in the functional capability of said first battery

6 A dual battery system according to claim 1, wherein said first battery has a first open circuit voltage and a first self-discharge rate, and wherein said second battery has a second open circuit voltage which is larger than said first open circuit voltage and a second self-discharge level which is lower than said first self-discharge level

7 A dual battery system according to claim 1, wherein said first battery is selected from the group consisting of a lead-acid battery, a nickel cadmium battery and a nickel hydπde battery.

8. A dual battery system according to claim 1, wherein said second battery is selected from the group consisting of a lead-acid battery and an alkaline battery.

9. A dual battery system according to claim 8, wherein said second battery is an alkaline battery.

10. A dual battery system according to claim 1, wherein said second battery is a non- rechargeable battery.

1 1. A dual battery system according to claim 1 , wherein said second battery is a rechargeable battery

12. A dual battery system according to claim 7, wherein said first battery is a lead- acid battery and includes a negative current collector and a positive current collector, said negative and positive current collector being substantially non-perforated.

13 A dual battery system according to claim 7, wherein said first battery is a lead- acid battery and includes a negative current collector and a positive current collector, said negative and positive current collector being 0.005 inches or less thick.

14. A dual battery system according to claim 7. wherein said first battery is a lead- acid battery and includes a positive plate and a negative plate, said positive and negative plate being 0.010 inches or less thick.

15. A dual battery system according to claim 5, wherein:

(a) said first battery is a lead-acid battery which includes a negative current collector and a positive current collector, said negative and positive current collector being substantially non-perforated and 0.005 inches or less thick; (b) said current direction regulator is a diode; and (c) said second battery is an alkaline battery.

16. A dual battery system according to claim 5, wherein:

(a) said first battery is a lead-acid battery which includes a negative plate and a positive plate, said negative and positive plate being substantially non-perforated and 0.010 inches or less thick;

(b) said current direction regulator is a diode; and

(c) said second battery is an alkaline battery.

17. A dual battery system, comprising:

(a) a first battery having a first self-discharge rate; (b) a second battery having a second self-discharge rate which is less than said first self-discharge rate; and

(c) an electrical circuit connecting said first and second battery in parallel.

18. A dual battery system according to claim 17, wherein said first battery has a first open circuit voltage and said second battery has a second open circuit voltage which is greater than said first open circuit voltage.

19. A dual battery system according to claim 17, wherein said first battery has a first open circuit voltage and said second battery has a second open circuit voltage which is lower than said first open circuit voltage when said first battery and said second battery are initially connected, but wherein said second open circuit voltage exceeds said first open circuit voltage at some later point in time.

20. A dual battery system according to claim 17, wherein said first battery is selected from the group consisting of a lead-acid battery, a nickel cadmium battery and a nickel hydride battery.

21. A dual battery system according to claim 17, wherein said second battery is selected from the group consisting of a lead-acid battery and an alkaline battery.

22. A dual battery system according to claim 21. wherein said second battery is an alkaline battery.

23. A dual battery system according to claim 20, wherein said first battery is a lead- acid battery and includes a negative current collector and a positive current collector, said negative and positive current collector being substantially non-perforated.

24. A dual battery system according to claim 20, wherein said first battery is a lead- acid battery and includes a negative current collector and a positive current collector, said negative and positive current collector being 0.005 inches or less thick.

25. A dual battery system according to claim 20, wherein said first battery is a lead- acid battery and includes a positive plate and a negative plate, said positive and negative plate being 0.010 inches or less thick.

26. A dual battery system, comprising:

(a) a first battery, said first battery being a lead-acid battery;

(b) a second battery, said second battery being an alkaline battery; (c) an electrical circuit connecting said first and second battery in parallel.

27. A dual battery system according to claim 26, wherein said first battery has a first energy capacity and a first self-discharge level, and wherein said second battery has a second energy capacity which is higher than said first energy capacity and a second self- discharge level which is lower than said first self-discharge level.

28. A dual battery system according to claim 26, wherein said first battery includes a negative current collector and a positive current collector, said negative and positive current collector being substantially non-perforated.

29. A dual battery system according to claim 26, wherein said negative and positive current collector are foils that are 0.005 inches or less thick. 30 A dual battery system according to claim 26, wherein said first battery includes a positive plate and a negative plate, said positive and negative plate being 0 010 inches or less thick

31 A dual battery system, compπsing (a) a first battery including a positive current collector and a negative current collector, wherein of said positive and negative current collector at least said negative current collector is 0 005 inches or less thick, and

(b) a second battery, and

(c) a circuit connecting said first battery and said second battery in parallel

32 A dual battery system according to claim 31 , wherein said positive current collector is also 0 005 inches or less thick

33 A dual battery system according to claim 31 , wherein said positive and negative current collectors each have two major faces, and further including a layer of paste applied to both of said major faces of said positive current collector and to both of said major faces of said negative current collector to yield a positive and negative plate, respectively

34 A dual battery system according to claim 33, wherein of said positive and negative plate, at least said negative plate is 0 010 inches or less thick

35 A dual battery system according to claim 34, wherein said positive plate is also 0 010 inches or less thick

36 A dual battery system according to claim 31 , wherein said first battery has a first energy capacity and a first self-discharge level, and wherein said second battery has a second energy capacity which is higher than said first energy capacity and a second self- discharge level which is lower than said first self-discharge level

37 A dual battery system according to claim 31 , wherein said first battery is a lead- acid battery 38 A dual battery system, compπsing

(a) a first battery including a positive current collector and a negative current collector, wherein of said positive and negative current collector at least said positive current collector is substantially non-perforated; and (b) a second battery; and

(c) a circuit connecting said first battery and said second battery in parallel

39 A dual battery system according to claim 38, wherein said negative current collector is also substantially non-perforated

40 A dual battery system according to claim 38, wherein said positive and negative current collector each have two major faces, and further including a layer of paste applied to both of said major faces of said positive current collector and said negative current collector to yield a positive and negative plate, respectively

41 A dual battery system according to claim 40, wherein of said positive and negative plate, at least said negative plate is 0 010 inches or less thick

42 A dual battery system according to claim 41 , wherein said positive plate is also

0 010 inches or less thick

43 A dual battery system according to claim 38, wherein said first battery has a first energy capacity and a first self-discharge lev el, and wherein said second battery has a second energy capacity which is higher than said first energy capacity and a second self- discharge level which is lower than said first self-discharge level

44 A dual battery system according to claim 38, wherein said first battery is a lead- acid battery

45 A method for maintaining the charge state of high power batteπes, compπsing connecting a first battery, a second battery and a current direction regulator to form an electπcal circuit wherein said first battery and said second battery are connected in parallel, said first battery being rechargeable and having a first energy density and said second battery having a second energy density w hich is greater than said first energy density, and said current direction regulator acting to prevent current flow from said first battery to said second battery

46 A method according to claim 45, wherein said current direction regulator is a diode connected in seπes with said first battery and said second battery

47 A method according to claim 45, wherein said connecting step further includes connecting a current level controller within said electπcal circuit to restπct the amount of current that can pass from said second battery to said first battery

48 A method according to claim 47, wherein said current level controller is a resistor connected in seπes with said first battery and said second battery

49 A method according to claim 48. wherein said resistor restπcts current flow from said second battery to said first battery to a desired low level which is sufficient to maintain the charge of said first battery but insufficient to participate in the functional capability of said first battery

50 A method according to claim 45, wherein said first battery has a first open circuit voltage and a first self-discharge rate, and wherein said second battery has a second open circuit voltage which is larger than said first open circuit voltage and a second self- discharge level which is lower than said first self-discharge level

51 A method according to claim 45, wherein said first battery is selected from the group consisting of a lead-acid battery, a nickel cadmium battery and a nickel hydπde battery

52 A method according to claim 45, wherein said second battery is selected from the group consisting of a lead-acid battery and an alkaline battery

53 A method according to claim 52, wherein said second battery is an alkaline battery 54 A method according to claim 51. w herein said first battery is a lead-acid battery and includes a negative current collector and a positive current collector, said negative and positive current collector being substantially non-perforated

55 A method according to claim 51 , wherein said first battery is a lead-acid battery and includes a negative current collector and a positive current collector, said negative and positive current collector being 0 005 inches or less thick

56 A method according to claim 51, wherein said first battery is a lead-acid battery and includes a positive plate and a negative plate, said positive and negative plate being 0 010 inches or less thick

57 A dual battery system according to claim 49, wherein

(a) said first battery is a lead-acid battery which includes a negative current collector and a positive current collector, said negative and positive current collector being substantially non-perforated and 0 005 inches or less thick,

(b) said current direction regulator is a diode, and (c) said second battery is an alkaline battery

58 A dual battery system according to claim 49, wherein

(a) said first battery is a lead-acid battery which includes a negative plate and a positiv e plate, said negative and positiv e plate being 010 inches or less thick,

Claim 59 A portable power supply comprising a first cell of a first type, said first cell being rechargeable and having a first peak amperage and having a first discharge rate, a second cell of a second type, said second cell having a second peak amperage and having a second discharge rate, said second peak amperage being smaller than said first peak amperage, said second discharge rate being slower than said first discharge rate

Claim 60 A power supply in accordance with claim 59, wherein said second cell has recharging means for recharging said first cell when said first cell is more discharged than said second cell

Claim 61 A power supply in accordance with claim 60, wherein said recharging means includes said second cell having a voltage decreasing less due to discharge current than a decrease in voltage of said first cell due to discharge current

Claim 62 A power supply in accordance with claim 59, wherein said first cell includes positiv e and negative terminals, said second cell includes positive and negative terminals, said first and second cells are positioned in a housing having positive and negative terminals, said positive terminal of said housing being connected to said positive terminals of said first and second cells, said negative terminal of said housing being connected to said negative terminals of said first and second cells

Claim 63 A power supply in accordance with claim 59, wherein said first and second cells are electπcally rechargeable

Claim 64 A power supply in accordance with claim 59, wherein said first cell is a first type of sealed lead acid electrochemical cell, said second cell is a second type of sealed lead acid electrochemical cell different from said first type of sealed lead acid electrochemical cell Claim 65 A power supply in accordance with claim 59, wherein: said first cell is a TMF lead acid electrochemical cell and said second cell is a traditional sealed lead acid electrochemical cell.

Claim 66 A power supply in accordance with claim 59, wherein: said first and second cells each have a substantially identical nominal voltage.

Claim 67 A power supply in accordance with claim 59, wherein: said first cell includes positive and negative non-perforated plates; said second cell includes positive and negative grid plates.

Claim 68 A power supply in accordance with claim 67, wherein: said plates of said first cell have a thickness less than 0.01 inches; said plates of said second cell have a thickness greater than 0.05 inches.

Claim 69 A power supply in accordance with claim 59, wherein: said first and second cells are electrochemical cells having a substantially identical nominal voltage and connected in parallel to form a power supply; and said second cell has recharging means for recharging said first cell when said first cell is more discharged than said second cell, said recharging means includes said second cell having a voltage decreasing less due to discharge current than a decrease in voltage of said first cell due to discharge current.

Claim 70 A power supply in accordance with claim 69, wherein: said first cell includes positive and negative non-perforated plates having a thickness less than 0.01 inches; said second cell includes positive and negative grid plates having a thickness greater than

0.05 inches.

Claim 71 A power supply in accordance with claim 59, wherein: said first cell includes spirally wound positive and negative plates; said second cell includes a plurality of substantially parallel plates. Claim 72 A power supply in accordance with claim 62, wherein: said housing has a box-like shape and completely surrounds said first and second cells and covers said terminals of said first and second cells, said housing includes a handle for lifting and carrying said housing by a human operator, said housing with said handle being a rigid unit.

Claim 73 A power supply in accordance with claim 59, wherein: said second cell has a higher energy density than said first cell.

Claim 74 A power supply in accordance with claim 59, wherein: said second cell has less cost for energy storage than said first cell.

Claim 75 A power supply in accordance with claim 59, further comprising a housing for holding said first and second cells, said housing including a handle sized for grasping by the hand of a human.

Claim 76 A portable power supply comprising: a first cell of a first type, said first cell being rechargeable and having a first peak amperage and having a first capacity; a second cell of a second type, said second cell having a second peak amperage and having a second capacity, said second capacity being larger than said first capacity.

Claim 77 A power supply in accordance with claim 76, wherein: said first peak amperage is higher than said second peak amperage.

Claim 78 A power supply in accordance with claim 76, wherein: said first peak amperage is higher than said second peak amperage with respect to one of size and weight of respective said first and second cells.

Claim 79 A power supply in accordance with claim 76, wherein: said second capacity is larger than said first capacity with respect to cost of respective said second and first cells. Claim 80 A power supply in accordance with claim 76. further compπsing a housing for holding said first and second cells, said housing including a handle sized for grasping by the hand of a human.

Claim 81 A method of using a portable power supply comprising the steps of: providing a hybrid power supply contained within a housing including a handle and first and second cells disposed within the housing; discharging the first cell; recharging the first cell with the second cell.