Just some general comments after living with the issue since 1990.

For bus starting batteries I will not purchase anything but Delco 1150. They are sealed and give at least 5 years of life unless you ruin them by letting them get down on voltage. No corrosion, no adding water, no problems. When the first one starts to go, it affect the other three, so it is best to bite the bullet and replace as a set.

Tom is right about how your coach is set up in more ways that one. The inverters are programmed for a specific battery type and gel, agm and wet cell all have different charging protocols or votages. My Heart inverters can be set with dipswitches if I switch battery types. It sounds like Tom's is programmed in.

Older coaches often had the batteries near the engine. My old coach was that way and the best service by far was from Delco group 27 maintenance free wet cell. Gel cells could not take the heat. If your batteries are away from the heat then AGM or gel is a good alternative.

Plan on five years, and if you recharge them before they get depleted they will go through a much greater number of charging cycles before they die. Any life you get after five years is a bonus.