I designed these years ago, and they've been holding up great. The side dovetails let you securely combine a number of them together. There's a sloped back, counter to a retaining edge on the front top that keeps the batteries from unintentionally sliding out. You can use the front contact “Charged” marking to keep track of which batteries are fresh. The flat, side-by-side arrangement allows them to sit comfortably in a side pocket.

I designed them to be print in PETG, 2 wall loops, 3 top and bottom layers.