Battery isolator charge vehicle battery on shore power

Yes, of course you can just run a large-gauge wire from battery bank #1 to battery bank #2 with a switch in it. Can be at the batteries or any place you have large-gauge wires from both banks in close proximity. And, this is the KISS way of doing it. Wire size and switch amp rating should be high so if one battery is deeply discharged, you won't over heat the "connection" with high-amp transfer.

But, it is not automatic and that is what most people value over KISS.