AA and AAA battery boxes with magnetic lid, space for 10 batteries while taking up the minimum footprint possible.

Lid uses (8) 3mm (diameter) x 2mm (depth) magnets, (4) magnets on the base and (4) for the lid. Magnets should friction fit into the holes but superglue is highly recommended to ensure they stay in place.

Print at 0.28mm and 5-10% infill for fastest print and good durability. Print time on my Ender 3 Pro was 3h45m for the AAA box and 4h25m for the AA box.

EDIT

Added a version of the AAA box with hexagon cutouts on all sides of the box.

This cuts the material usage and print time significantly. I am not sure if this version of the box will hold as well as the other versions but it should be more than usable. This also adds a easy way to see how many batteries are in the box without having to open the box up.

The version is also kinda ugly so be aware of that :)