[The Newell]

Often but not always chargers will have a setting for AGM that is different than for wet cells. Mostly they're the same but the higher voltage used in wet cell systems for equalizing is something you do NOT want to feed to an AGM. If you don't have an AGM setting available, maybe another charging system is something to consider. they shouldn't gurgle, and if steam is coming out, you're loosing irreplacable electrolyte and again, killing them. Their vent system is "emergency only" and should never open under normal circumstances.