The ornamental design for a rechargeablebatterypack, as shown and described.
FIG. 1 is a perspective view of a rechargeable battery pack showing our new design;
FIG. 2 is a top view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a left view thereof;
FIG. 6 is a right view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a perspective view of a rechargeable battery pack as a counterweight with a telescope mount thereof. The broken lines showing the telescope mount in the drawings are included for the purpose of illustrating environmental structure and form no part of the claimed design.