I have a couple of 100 amp-hour wheel chair deep cycle AGM batteries in our Class C. They're coming up on their 7th year this fall. The stock Parallax fixed voltage converter and engine alternator is about all they see. However, on our last trip this year they got some charging from a very old 2/10/50 cheap "charger/starter" set to it's 50 amp starting setting.
I regularly take them down to around 50% state of charge. From this state of charge, the main engine alternator takes them to full charge in around 5-6 hours of driving ... according to the dash ammeter I installed with it's shunt in the their main negative terminal cable. I can tell when they're fully charged because their current acceptance reads right around zero on the ammeter. When they are being charged by the Ford engine's 130 amp alternator, the AGM batteries are connected directly in parallel (via a heavy duty solenoid with silver alloy contacts) with the main engine's wet cell starting battery.
These wheel chair AGM 12 volt deep cycle batteries have been trouble-free and maintenance-free the whole time.
