PLA 0.2mm layer height. Infill 95%.

https://www.thingiverse.com/thing:1815758

Shape the pads and install them in the battery socket.

Glue the battery connector to the battery case.

Cut the case with the hack saw until you happy with the over hall shape of the assembly.

Solder the pads of the socket with the connector "the positive to the positive" and "negative to the negative"

Insulate electrically the solder joints with some rubber.

Glue the both half together