Hey!, Here's a thought:

Optima Batteries(and probably others as well)produce a battery(In Designer colors)that is sealed, so no outgassing occurs on charging(Important, as a neighbor lady was killed when a battery on her mobility cart exploded in her home during charging due to outgassing of the battery, accompanied by some errant spark from somewhere-so says the News-apparently she was unable to walk away from the house fire)

But perhaps a "Designer" "Safe" battery wouldn't offend!?

It may not work well in your application, but might give a heads-up for any other readers considering a similar set-up with batteries in the home.

We had one of our boat batteries go "poof", rupture a cell and splatter acid in a relatively confinned space when-oops-we failed to turn off the charger prior to disconnecting it from the battery!

We were younger then! And so was battery technology!!

Still....