There are many battery holders for Parkside X20VTeam here. I made this one few years ago. Tested with PAP 20 A1/A3 batteries. For mounting purpose, you can use PDF template (print with 100% scale) and 3x D3,5mm Wood screws.
My printing setup:
Material: Prusament PETG
Nozzle diameter: 0.4 mm
Layer height: 0.2 mm
Infill density: 20% (Gyroid)
Support: Yes
Filament used: 18g
Print time: cca 1:30h
EDIT: Added model with two screws
The author marked this model as their own original creation.