I use a 81mm mortar ammo can, was like $30 to my door from Amazon. Will easily hold 3 full size batteries with room to spare. I lined it with fire insulating blanket. It should contain a mishap if a battery goes south on me, or at least minimize the damage. I keep batteries and charge inside the house.
I forgot to add details. I actually looked for a cabinet for nearly 3 months. Zoro had a sale AND free shipping. I was shocked by the deal and jumped on it. Listed now for $508.87 plus shipping. I paid $270 shipped. Which was $100 less than what i saw used being sold for. Seemed to good to be true but sure enough free shipping too. I have seen them for $400 shipped, using Google search tools i got at leadt one listing a day until zoro popped up
It ships free but I see the price is up $70 from a year ago.
My main problem is garage floor space. I'm going to have to do some major reorganization to find space for it. For now, the ammo cans fit nicely under a steel storage rack.