You said "1) They don't puke acid fumes all over and corrode everything nearby, including themselves." My experience says that is just an old wive's tale used to justify expensive new batteries.

My four T-105s and GRP27 are all in unsealed containers that are directly below and within 12" of my Battery Charger/Inverter / Current sensing shunts / Solar Controller / Towed Generator controller / EchoCharger / Terminal Blocks for all DC connections / ICOM antenna tuner / copper grounding foil for HF radio / Ardic diesel heater (which contains a lot of electronics). There is absolutely NO SIGN of corrosion or damage after eight years. When I swapped out the seven year old T-105s the cases were in perfect condition and there was not one indicator, not one crystal, of corrosion on any battery or the cases.

Our boat has done some heavy sailing and has spent a lot of time heeled WAY OVER. Twice she has laid on the beach at over 60 degrees heel for over eight hours. Not one drop of electrolyte spilled from any of the five batteries. I have never seen any sign that a well made flooded acid battery leaks thru a properly installed battery cap.

You said: "2) They don't self discharge at about 10%/month."

A 20 watt $100 solar panel will keep even my 675 amp hour battery configuration fully protected against self discharge if I never use the boat. But, when does a month go by that you don't use the boat?

Justifying AGM batteries based on reduced maintenance also makes little sense to me. In eight years - the only maintenance I have ever done to my T-105s is replace water once every four months - that takes less than 15 minutes. What maintenance am I missing? I have never equalized my batteries and have never seen any need to. If the batteries are fully recharged on a daily basis - no sulphation occurs and equalization is not necessary.

Charging rate / bulk acceptance capacity is also a mystery to me. My T-105s accept all the power from my 135 amp alternator with no problem, even in 105 degree ambient conditions - how much bigger alternator are you talking about? Lead acid can accept 25% of their amp hour capacity during the bulk stage - that is 56 amps per pair of T-105s. So a 450 amp hours of capacity can absorb the practical maximum output from any "typical" DC power source on a sail boat. If you have a bigger charging source then I imagine you have a bigger battery bank that can accept more current - my bank of T-105 could absorb 175 amps of charging current - but where am I going to find that much DC current?

I am sure AGM batteries are wonderful things to have but I still see no reason for them based on corrosion, leakage, maintenance, charging rates, and most importantly cost. Just my opinion based on a lot of experience.