I like Wizavich's magnetic battery case, but I found it just a bit difficult to remove batteries, so I remixed it to have alternating height for the batteries. In the process the shape went from square to oblong, and the battery count went from 16 to 15.

Magnets are 6x2mm. I use a small artists' spatula to hold each magnet over the recess, then tap it in with a small hammer. I printed the cases in PETg, so its resilience may help with accepting and holding the magnets.