NEVER, NEVER, NEVER equalize these batteries against the manufactures advice. AGM batteries are known in the industry as VRLA (valve regulated lead acid). These batteries have a stringent charge requirement to prevent a condition known as thermal runaway at high temperatures and to maintain full charge at low temperatures. Without the proper charger, these batteries have been known to explode. Admittedly, these explosions have happened, as far as I know, only in industrial settings. However, some of those that did where in controlled environments, i.e. air conditioning. Most have happened in huts without adequate air temperature control (ever been in your boat in the sun while it’s in the slip). I have never heard of one happening on a boat, but there is always a first time. I have yet to see a marine charger with temperature compensation (lowering the float or charging voltage at high temperature and raising it at low temperature). They may be out there, if so, if you insist on having AGM batteries or sealed batteries you should invest in one.
Sealed batteries use to be the craze in the early 90s with the maintenance free battery for your car. When is the last time you have seen a new car with a maintenance free battery as standard equipment? Now granted, auto batteries are not deep cycle, but the chemistry is the same.
Replace your batteries. Do NOT try and revive them. I have been designing chargers for the telecommunications industry for over 20 years (mostly VRLA batteries) and will NOT have them on my boat. A good set of wet cells (notice good, i.e. deep cycle, thick plates. Etc.) will outlast VRLA every time if maintained properly.