I've thought about sequestering all battery-containing devices into a metal cabinet of some sort. Would this increase safety or cause a cascade failure because of the concentration of batteries?
Discussion
It depends on the chemistry involved.
And if you have that much juice, a metal cabinet might do some good, but it can't stop the combustion.
Visually inspect the cells, anything looking sus, bury it in a metal pail with a locking lid, filled with sand.
They do sell fire retardant bags for storing and charging lithium batteries.
https://www.youtube.com/watch?v=Rv_3vwSZmzA Ammo cans.
Excellent! Thanks! Harbor Freight has them...