The ornamental design for a batterypack, as shown and described.
FIG. 1 is a top, front, and right side perspective view of a battery pack according to my new design;
FIG. 2 is a left side elevation view thereof;
FIG. 3 is a right side elevation view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a front elevation view thereof; and,
FIG. 7 is a rear elevation view thereof.
The dash-dot-dash broken lines represent boundaries of the claimed design and form no part of the claimed design. The equal-length broken lines depict portions of the battery pack that form no part of the claimed design.