My lifeline 100ah battery still has the same AH capacity if not a bit better than it did when it was new, almost 5 years ago...
I test my battery's capacity about every 2 mo. I also monitor via my trimetric meter the amp hours drawn from the battery v/s the battery's voltage 2 times a day when camping.
My trimetric also records the total "cumulative" AH.... I zero'ed it when my Lifeline was new. So far that Lifeline has produced over 5,000 AH...
It is maintained by my Progressive Dynamics 9260... Also by my 200watt solar system when the camper is in the sun. There is no sun in my Bigfoot Cave so I have to rely on the PD to maintain. When we are out with our camper I never plug into shore power unless I want to use electric heat, then I run the fridge on 120vac.
There are many folks using PD's, Iota's and Boondockers to maintain AGM's and have had "0" problems....
I will never go back to Flooded Wet Cells.... They require maintenance that is really difficult on the Bigfoot campers.... Pulling the batteries out of the battery compartment is a royal pain in the AXX. Then the mess of watering and measuring Specific Gravity.... UGGGG.
I have not pulled my AGM out of the battery compartment since I put it there..... I do look at it to check the connections periodically...
As for FWC's I ran 2 group 24's for quite a few years... They would last about 1.5-2.0 years...
Have had this camper 14 years.
I only have 1 battery now.... After I installed led lights, led tv (had a tube type before), Wave-3 heater I found I did not need 150-200 AH capacity from my batteries. 100AH is fine.
We use and average of 10-20/day..
Jim