Minimalistic keychain box for hearing aid batteries

I wanted to have hearing aid batteries always with me when away from home. Keys on a keychain are always with me, but none of the commercial solution suited me - mostly they were too big. So I set out to create and print my own.

The box is just big enough to fit the batteries inside and to have a sturdy loop. The box and sheath feature a small catch to keep it closed, but the catch wears over time, in around 2 years of my use. But you can always print another one…. I've included boxes and sheaths for 312 and 13-size batteries. 

The box in pictures was printed on a Prusa Mk3S with Filamentum crystal blue PLA, so that I can always see if the batteries are in the box and if they are fresh (if I cannot discard batteries safely, I put them in without the removable tab). They were printed with the new Prusaslicer with Arachne perimeter generator and 0.6mm nozzle and the function perfectly.

If your printer has different tolerances (quite important for the functioning of the catch), I've also provided an OpenSCAD model so that you can tweak the two tolerances at the top. It is likely that just changing “x_tol” by 0.1mm should do the trick.