Portable Battery

FIG. 1 is a perspective view of a portable battery showing my new design; FIG. 2 is another perspective view thereof; FIG. 3 is a front view thereof; FIG. 4 is a back view thereof; FIG. 5 is a left side view thereof; FIG. 6 is a right side view thereof; FIG. 7 is a top plan view thereof; and, FIG. 8 is bottom plan view thereof. The broken lines in the drawings depict portions of the portable battery that form no part of the claimed design.