If that is all you use the battery for any battery will do, in fact you can probably scale back to one battery.
But, unless you have a battery disconnect switch there are certain parasitic draws that run off the battery 24/7/365. For example the radio and I think the circuit board in the refridgerator and furnace.
It will decease battery life to fully discharge.
Sail on silver girl. Sail on by. Your time has come to shine.