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; and,
FIG. 7 is a bottom plan view 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.