I have had 6 Volt AGM batteries in my boat in the Caribbean for 2 years. Somehow my Link 2000's have allowed my Freedom 25 to apperantly overcharge the batteries as they are buldging and wont hold a charge. I am told that 90% of the crusiers in this area use the Trojan 105's as they work the best and are half the price. Someone said that because the area were my battereies are located is not well vented, that I should not use the Trojans. Any advice on this matter?
Sounds like your charging system needs to be gone over
Your battery compartment(s), no matter if you have wet cell or AGM are required to be vented. Wet cell batteries produce hydrogen gas while charging and lots of it if they are being overcharged.
AGM batteries only produce hyrodgen gas if they are being overcharged as what appears to have happened to yours. People( builders, some repair techs and those not in the know) sometimes think that because they do not produce hydrogen when all is working properly, they can be put anywhere. There are a number of cases where AGM types have been stuffed into unvented compartments and have overheated and exploded. A bad experience if you happen to be nearby or on top of them (as in under a bunk). It is ok to have them under a bunk, just make sure you have a proper ventilation system set up.
Both types of batteries have different charging requirements which your system (Link 2000) should be able to ajusted to when it is set up properly, which also includes temperrature compensation during charging.
ABYC Standard E-10 covers the requirements for proper procedures for storage batteries, including the Federal Regs. This will make your insurance company happy as well.
Request that all work done on your vessel be done in accordence with ABYC Standards and applicable Fed (CFR) regs as well.
ABYC Master Tech.
Steve and SD are correct that you will get more bang for your buck with wet cells if you maintain them. On the other hand if your system is set up properly for the you will get very good service with the AGM batteries and not have to be adding water as you will have to with wet cells.