Originally Posted by cardude01
So maybe the batteries are charging, but just old and weak?
Or maybe the batteries are fine and not charging once drawn down below a certain level.
This is what you need to figure out. You can guess, then replace parts and see what happens. Or you can do some test and experiments to really diagnose the problem.
Isolating each battery, checking its voltage, and load testing is a great step to assess the batteries themselves.
But even if you find one or more bad batteries, I'd carefully check the engine charging system, especially with respect to the Duo Charge (I think that's what it's called) and what happens if it starts shutting down when more than 30A is called for. If that happens, how will your batteries ever get recharged? If nothing else you need to know how to detect if this is happening, and have a way to recover from it.