Joe,
For starters, here is the situation: The "maintenance free" group 31 batteries that are in almost every Prevost out there, ARE NOT sealed batteries. They are, in fact, vented to the atmosphere, and thus evaporation occurs. The only truly sealed batteries are the Valve Regulated Absorbed Glass Matt (AGM) or Gel batteries. To make matters worse, charging flooded vented liquid lead acid batteries will cause gassing, so this type of battery must be observed for electrolyte level while under a charge, which you cannot do with the Prevost standard start batteries.
I just simply tell everyone with a Prevost that comes into our facility to either treat the start batteries as disposible and change every 2 years if you live in the south, or buy AGM's and replace them every 5-10 years, as they actually wear out.
Ben Cummings
U.S.A. Luxury Coaches, LLC
Clearwater, FL