I also use the ammo case. I get them at the Army/Navy store, cheap about $8 for the small one and $12 ish for the large one. I put vertical separators down the length to store the packs vertically. I put a small piece of red tap on one end and green tap on the other. The charged packs have the green side up, once used I put them in with the red side up. This save lots of trouble keeping track of charged packs at a contest when things get going (always at the contest when things go nuts, always), cheap insurance.
In the small case I get six packs (battery's) 4S 3950 size and smaller, twelve in the big one (double row).
Best, DennisT