Bosch GSR 12V battery.

thingiverse

For LiPoly 3x18650 battery replacement of the original NiCd, follow these instructions. Print your model without support, as it features an empty "stem." Be cautious of the 3mm holes for the cap and approximately 3.5mm holes in the cap; use self-tapping bolts for secure attachment. The cap serves to hold the main charging port (T-deans) and a bundle of balancing wires in place.