A display device has a time-constant circuit and a switching element such as a transistor for supplying the voltage of a battery to the time-constant circuit when a battery check key is pressed. A microcomputer measures a time interval from a time when the voltage of the battery starts being supplied...http://www.google.fr/patents/US5424722?utm_source=gb-gplus-shareBrevet US5424722 - Device for displaying remaining electric energy of battery
Device for displaying remaining electric energy of battery
