Use auto battery in permanent parked 5th.

[Cypressloser]

Originally Posted by wa8yxm

You can use any type of battery so long as you are only using it to filter the DC. Starting (Auto) MARINE/deep cycle (WHat you most likely hae now) or DEEP CYCLE

The difference between them is basically how far you can run 'em down before they start fast aging.

Starting batteries like to be kept full, 80-90% State of charge MINIMUM

MARINE/deep cycle can go a LITTLE lowerm say 75-80%

DEEP CYCLE to 50 %

Absolutely, why make it more complicated than it needs to be.
Even a starter battery can go for 6 - 8 years in this scenario.

[mrgrayaz]

Why are you even replacing the old ones? They can basically have no useful capacity left in your scenario and be useful enough to level out the lights and converter voltage.