So do I..
I also run on both allways. I only have 2 75amp car batteries, (one for the engine one for the house)..allways used car batteries, they're lighter and cheap. And if damaged before the warranty of 2 years expire, I take them to the supermarket where I bought them and get a new one.
I have a 25 amp for the VHF (in europe the VHF needs a separate battery by law), and a 50 amp for the anchor windlass in the front.
One day we forgot the lights on and left, and when we returned we had no battery to start the engine.
So I brought the windlass bat and started the engine..then charged the 2 main ones...