FIG. 1 is a front, top, and right side perspective view showing our new design for a battery charger in full lines and broken lines, wherein the broken lines are for illustrative purposes only and form no part of the claimed design;

FIG. 2 is a left side elevational view of the battery charger according to FIG. 1;

FIG. 3 is a rear elevational view of the battery charger according to FIG. 1;

FIG. 4 is a bottom plan view of the battery charger according to FIG. 1;

FIG. 5 is a top plan view of the battery charger according to FIG. 1;

FIG. 6 is the front, top, and right side perspective view of FIG. 1 with the broken lines removed;

FIG. 7 is the left side elevational view of FIG. 2 with the broken lines removed;

FIG. 8 is a rear elevational view of FIG. 3 with the broken lines removed;

FIG. 9 is the bottom plan view of FIG. 4 with the broken lines removed; and,

FIG. 10 is the top plan view of FIG. 5 with the broken lines removed.