What is claimed is the ornamental design for portable battery charger, as shown and described herein.
FIG. 1 is a ¾ view of a portable battery charger showing the new design;
FIG. 2 is a top view of the portable battery charger shown in FIG. 1;
FIG. 3 is a bottom view of the portable battery charger shown in FIG. 1;
FIG. 4 is a right side view of the portable battery charger shown in FIG. 1;
FIG. 5 is a left side view of the portable battery charger shown in FIG. 1;
FIG. 6 is a front view of the portable battery charger shown in FIG. 1;
FIG. 7 is a back view of the portable battery charger shown in FIG. 1;
FIG. 8 is a front view of the portable battery charger shown in FIG. 1 with the front cover opened, whereby the broken lines shown in the drawing are for the purpose of illustrating unclaimed portions of the power bank and form no part of the claimed design;
FIG. 9 is a back view of the portable battery charger shown in FIG. 1 with the back cover opened;
FIG. 10 is a right side view of the portable battery charger shown in FIG. 1 with the front and back covers opened; and,
FIG. 11 is a left side view of the portable battery charger shown in FIG. 1 with the front and back covers opened.