I'm with Nick.
We have 12 x AGMs that we installed 4 years ago with battery balancers to ensure the voltage across the series batteries stays equal and we have had ZERO problems so far. Elyse has 600W of solar and a wind generator and when we are at the dock the mains charger is on as well. We keep the frig and one freezer running all the time.
At sea we use the genset to charge the batteries and other 220V requirements. We rarely let the batteries drop below 85% and are religious about not overcharging them. We have a 3 stage external regulator on the engine alternator to ensure the right charging profile, AND I installed a switch in the cockpit so I can disconnect the field wire at the regulator for when the batteries are fully charged from being at the dock and we make short trips to the fuel dock or the travel lift so the alternator doesn't ramp up to 28.8 V every time the engine is started.
I am sure that internally regulated engine alternators on boats are what kills house batteries. Those internal regulators are really designed for automotive applications mainly charging start batteries, they ramp up to 28.8V and stay there - all day - no good for deep cycle batteries.
Its an endless discussion it seems!