Modified the original to convert into staggered battery storage for AA, AAA, and 9V batteries and modified a few other things.
The photos are not the final design. It's there just to show the staggered stack.
I'd recommend not dropping the batteries from the very top.. the front slot is there so you can lower the batteries down. It probably doesn't matter but better safe than sorry.
*Update - Added 18650 Battery Stacker.