Battery Flap Replacement for MEI 100 Receiver (in-ear monitoring system from LD Systems)

This 'thing' is a replacement battery flap for the LD Systems in-ear monitoring receiver MEI-100-R (for the MEI 100 series):
https://www.ld-systems.com/en/series/mei-100-g2-series/

Print with 100% infill / PLA / 0.075mm layer height / put some Aluminium tape on the inside to connect the batteries in series