Just spent the evening modelling up the existing battery cover, so I can check dimensions before I grab a copy and modify it in CAD.

I'll do a test print now and see how my measurements are.

The model in OnShape.

The model in OrcaSlicer before printing

Should take just over 30mins to print on my Flashforge Adv 5m in PLA, though I probably won't use PLA for the final build for thermal reasons.