The ornamental design for a batterypack, as shown and described.
FIG. 1 is a left perspective view of a battery pack in a secured position;
FIG. 2 is a left side view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a top view thereof; and
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a left perspective view of a battery pack in an unsecured position.
The broken lines illustrating a wheel hub in FIGS. 1-7 are for the purpose of illustrating environmental subject matter that forms no part of the claimed design.