I suggest you get two GC2 batteries. They are cheap and copious and a very common choice.
I would suggest you avoid AGMs as house batteries, they are supposed to never need water but they lose some during charging or harsh use and there is no way to put it back. I also very strongly suggest that you install a master battery switch if there isn't already one, and that you get a battery protector like the one
at this link.
I guarantee you that you will leave that master switch on sometime and the batteries will run flat, if you don't have the protector. If they work at all after that they are never the same.
This is what sealed batteries were originally meant for. The acid would not run out while the car was vertical. Of course lots of people want maintenance-free batteries.
