This back plate fit with the Muzi Works BB15 BASE System Battery, but I did have to nudge it higher onto the board a bit.
If space is a concern, I've uploaded a 2x inserts version that should let the battery stay exactly the same as the original case back.
The author remixed this model.
Modified from Nikolai Schauer's design. Added 4 holes for M3x3.0 heat set inserts from CNC Kitchen.
Also adjusted the back screw holes from 3.6mm to 3.75 to help make it a bit easier to insert the included screws.