^^^Thass what we do. Can leave it off a couple months and it'll start the genset. Chassis battery will start the V10 too...
I finally (after years of frustration) installed drawer slides on the battery tray. Checking is now SO much easier. Single 12V Deep Cycle WalMart battery. It would be MAJOR surgery to adapt to dual batteries. An OP, former Moderator, did that on his Jayco and made a beautiful job of it. I can see doing that for lots of boondocking and wanting 6-volt batteries. For us, one 12V has been fine. Previous coach had two 12V and nothing but trouble. One was always boiling or going dead, etc. etc.