I have now switched out 12 FLA battys to AGM between boat and MH.
Boat AGM serves house and start and charged while running from eng alternator - only change was setting shore charger to AGM profile.
MH house bank AGM with chassis still original sealed FLA. Also just changed shore charger profile setting.
I'm no expert but have done some digging & reading about alternators and AGMs. My understanding is the charging profile is very close between FLA and AGM with the biggest difference ( tenths of a volt) is in the float setting where the battys are simply being maintained with little amp flow to the batty. If too high over an extended time it can affect AGMs negatively.
Alternators (V regulators) do not normally provide a multi stage charge like shore chargers the control turns the alternator on or off based on the V of the batty. So in a sense there is no "float" where the alt remains charging at a reduced V over an extended period (days) like a shore charger.
Bottom line is AGM replacement in a chassis application should be no problem.
Some newer vehicles are putting AGM in their higher end trim levels with more bells & whistles and auto idle feature. I have only checked one but the alternators were the same and I believe internal V regulatio is the most common in auto alts.
Don & Marge
'13 Newmar Ventana 3433 - '14 CR-V TOAD
'03 Winnebago Adventurer 31Y - SOLD