Trouble is they do need to be fully charged as soon as possible after any discharge cycle. easier if you have plenty of solar. If they stay in a partial state of charge for any length of time they will sulphate, so gradually loose capacity.
Most folk don't notice this capacity reduction so are happy, but if you were to do a proper capacity check, you might find that 95AH has become 70AH, so when you use 95AH expecting to be at 50%, you may actualy be discharging to a lower % than you think, alternatively if judged on voltage, you might find 50% is reached quicker than in the past!
Our AGM 4*185AH bank lasted two years, and then I found it had lost significant capacity. Whilst OK on small loads like the lights or water pump they couldn't handle anything big like a small microwave, so were replaced. 2 other of the same type went west in much the same period that were used on a thruster installation. All attributed to periods of time left at partial state of charge, or incomplete charging. We had no solar, and if away for 6 or seven weeks it was unlikely they would get a full charge unless we visited a marina. Tehy would take hours with the generator to fully charge (the last 20% odd), so not practical.
