simple tpu condom like sleeve best printed in a flexible material to transport spare liions in your pocket avoiding a short circuit.
should fit tight if printed flexible. should print upsidewards.
Reworked the double (file ending on 3) to fit a little looser since the single on the first print with amazon basics TPU sits a little to tight. Added number 4 with a bigger handle to attach to a keychain or something. or use it as a Lever to pull the batteries out easier.
Have been using to of them for almost 6 months now and they work perfect. after a week or two the get perfect and easy to use.