I maintained a group 24 AGM at a constant 15.6 volts, 24/7 for three months in the antelope valley in 1992. At the end, it had not lost .3 oz of weight. The scale I used was assigned a registration number certificate with NIST. The popoff valves were intact. It was not a Chinese battery.
Out of (perhaps) ten batteries I tested for RAMCAR battery, the lowest voltage encountered that popped an overpressure vent was lower 17's.
So absurdly high that I have seen few legitimate AGM vented batteries. Warpage of plates is the usual suspect in AGM overcharging. And plate deformation is sure and certain death.
Anyoneone who cannot maintain the common sense to avoid mistreatment of posessions needs a room key not an RV key.