Sturdy Hearing Aid and Battery Case

I needed a hearing aid case to protect my hearing aids when I travel. I figured that I'd add storage capability for four batteries (315), and enough room to store a silicone pack from a filament box.

As a fun note, my friend asked if it was waterproof? I took this as a challenge and added a 1.7mm round groove in the cap, cut a length of TPU filament to the right length, then Superglued the ends to form an O Ring.  It is completely unnecessary, but it works incredibly well!