AGM batteries WILL VENT (out gas) under "extreme overcharging". If they did not, they would explode.
Recombinant caps that change vapor back into liquid really subdues pressure build up. You've got to, with your own hands, work with these batteries to get a better understanding of the subject. And the likelihood or not of malfunction.
I have rehabilitated many different group sizes to above 17 volts and only two, vented. Both were not Lifelines. Do not rehab an AGM while still in the rig.
The last battery explosion I saw was on an older Tioga. Owners started the generator, connected a transformer battery charger, then ventured to a beach bar. Gor plastered. People started yelling. They heard a pop and then a sulfur reek covered the beach like Yellowstone Park. it was unbreathable near or inside the rig. The batteries were outside.
What a mess.
They were in no mood to discuss anything the next day. They fiddled with the batteries, got a jumo start then headed north.
