I replace a LOT of AGM batteries not just Lifeline but Deka, Optima etc. and with boats on moorings, recharging by alt only, the life is short. They average around 2-4 years on mooring sailed boats though I have seen them die sooner.

The big issue I have with AGM's is that when they fail they often give little warning and fail catastrophically... I have one customer who had a great weekend with his wife and family just the week before and they ran whatever they wated and started the motor just fine. The next weekend there was no wind so they motored for three hours. When they got there they tried to hail the launch but the VHF would not work. The owner realized he had dead batteries so in a hurry to get to shore and met friends he used the "combine" feature. The dead house bank then took out the starting bank and all batteries were flat dead. I charged then tried to equalize all 5 batteries. The best CCA test I could get was 7 CCA out of the house bank, yes SEVEN cold cranking amps, and 73 CCA on the start bank. The batts were beginning their fourth season. He's now back to deep cycle wets and has finally added solar...

I've spent a lot of time on the phone with Justin G. at Lifeline and the information on the Morgan's Cloud site is 100% accurate. Justin backs this up for marine applications and he's not afraid to discuss it. When I have to explain to my customers that their "maintenance free" batteries are going tor require 8 hours tied to a dock as often as once per month they usually wind up going right back to wet cells, though a few choose GEL's...

If you tie to a dock each night AGM's can be good but of you sail off a mooring and do not supplement with solar or wind it can be an $$$$ ride.. If I had to guess at how many AGM batteries under four years old I replaced this summer alone, and I have four more 6V lifelines to do this week before a boat heads south, I would guess it to be close to 24-26 batteries. On the other hand most of the wet cells I replace are 5-7+ years old and often coast a third of what the AGM's do. GEL's I have seen go 10+ but they need constant attention so that you don't accidentally over charge them. I had a customer ruin a 1 year old set of $1400.00 GEL's by using a POS Schumacher Ship n Shore to "top them up" over the winter. On the Schumachers GEL setting the batts were seeing over 15 volts!!! Cheap chargers and expensive batteries are a bad mix.. The Oddysey batteries seem promising but the oldest bank I know of on a customers boat just ended year three so I can't comment on longevity...

Good old wet cells are still a great value despite their flaws.. Right now I am paying about $0.72 / Ah for 6V deep cycles...