With my increasing collection of electronic devices . . . e-caller, trail cameras, night lights & regular high-intensity lights all of which use rechargeable LiON batteries, I needed a safe & secure method to transport spares during my various endeavors. Battery boxes are available, but those I found were capacity-limited. The light went on yesterday as I re-organized my storage room (no pun intended) . . . all of my 3.7v batteries fit quite nicely & most securely in a 12/20 ga 3" plastic shotshell box, of which I have several. Just thought I'd pass this along. I'll find the right cartridge box to accomodate AA's.