The ornamental design for a batterybox with solarpanel, as shown and described.
FIG. 1 is a perspective view of a battery box with solar panel, showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is an enlarged view of a circled portion 8 thereof.
The broken line shown are included for the purpose of illustrating portions of the battery box with solar panel which form no part of the claimed design.