You don't need Sandia or Lawrence Livermore Labs to keep your batteries healthy.
Charge one per week until the one half percent brick wall is encountered at 14.4 volts. THIS IS THE BIG KEY TO IT ALL
Don't allow the bank to fall to more than 50% amp hours extracted
The linchpin of your problems is you do not have near enough amperage to saturate charge your batteries when using the generator.
I have 4 L16s and they suck the equivalent of 215 amperes saturated charge max. And they are not even AGM.
When I hose the 31XT and 31 2-story Lifelines they suck close to TWO HUNDRED AMPERES total @ 14.4 volts
Generator charging is a PITA. Why suffer hours of charging to prevent well cell sulfation or AGM sulfation? Put that damned generator to work!
Your inverter is screwing you with a casper milquetoast charging protocol. Fix the SOURCE of the problem not the RESULTS of the problem.
Any AGM battery that has not been overcharged yet has lost weight, has DEFECTIVE VENT VALVES. About as likely as a driver's door falling off a new Rolls Royce when dealing with Lifeline.
