My car keys use these 3V button cells so I made a little keychain holder that I can put spare batteries in and always carry with me.

Holds 2 x 3V button cell (⌀20mm x 2,5mm each)

Print in PLA, the two halves snap together firmly once cooled down. To separate them, twist them so that you can use the little tabs to lever it apart. Should be pretty self explanatory.

Feel free to use this for anything you like, including selling it. No attribution or compensation required :)