I think the firey said they were partly lead acid? 3 different banks of batteries. He probs got a dozen from supacheap and hooked them up, didn't like what the proper one's cost.
I don't think it would be too smart to install these in a confined space, as with gas water heaters there's rules where they can be mounted, and a fireproof barrier placed between the unit and anything flammable. Nothing difficult about that.
