I keep mine here
^ Not sure how you British folks get any bullets out of the end of yer rifles with those yellow thinggys ^ on the ends, but whatever floats yer boats. BTW, lil heads up, if you duck yer heads down just a tad more yer less likely to get it blown off. Seems like batterys would be the least of yer worries.
Over the many years I’ve been using rechargeable li-ions, I’ve found two that vented in storage.
No fire, just a brown stain around the positive end and inside the box where I had them stored.
I’ve also found evidence of one leaking while on a charger. These were all years ago, not recent.
I don’t trust them to be reasonable about how they behave. There are a lot of places in China making li-ion cells, using whatever plastic film membrane they have handy to roll up the components.
The quality of the membrane is critical to safety with these cells.
I’ve had two that discharged until dead, while stored. I never did figure out why. I don’t think they vented though.
Wow this came back?
I only store 18650’s and those go in a hard plastic storage container with 25 separate individual compartments- it’s a repurposed 12ga storage box.
Protects them quite nicely from any physical damage.
WOW, same here. Some will also store the 21700 but the MTM 12ga won’t with it’s anti-rattle ribs.
Definitely more people who do it because I stole the idea from somewhere.
I only store nimh in these sizes instead of any type of lithium, but storage boxes for .500/.460mag work well for AA/14500 and storage boxes for .44/.41mag work well for AAA/10450.
Have to keep my eneloops organized.
I got this idea from somewhere here on BLF. Lipstick holder from The Container Store. Works great for 18650 and 21700 batteries.
I keep mine in the closet with my spare toilet paper, paper towels, and printing paper! 
I store my cells in the same container as I do my other Lipo batteries, for my RC cars. I put them inside their plastic container and then put them in a metal ammo case. I remove the rubber o-ring that holds the ammo can sealed. To prevent any possible explosion from gasses, and, or, fire. In case any cells go kaboom. you can buy the metal storage case on amazon. that’s where I got mine.
I find ammo cases work better. Plus the cells stay inside the container.