Dual batteries
I hate to use the "F" word here, by the Ford 'Camper Special" truck I had years ago had two batteries under the hood. One solely for the truck, the other solely for the camper. The setup from the factory kept both charged while driving, but they were separated otherwise so the camper battery never drained the truck battery.
You might do the same. One battery solely to start the car, the other solely for the accessories.
