Wouldn’t a generator a few hours a day keep them charged?
It’s the repeated process of charging and draining on a daily basis that is going to “wear out” the batteries. That is why you need expensive batteries to handle that kind of “up and down.” Most batteries are not for such prolonged use. Marine and auto batteries are constantly being trickle charged through the engines. That is why I thought solar which would trickle a little charge all day into the batteries to keep them topped off.
I would think something like a Bluetti 200L or Jackery 2000 Explorer could do the job. While the engine is running it can be recharging and it will have enough power to run a microwave or small AC unit.