When we first outfitted the boat these were the be all and end all of batteries. Since, I've now learned my lesson. Much of what Lifeline and other AGM makers were saying ends up just plain wrong. Ironically on Lifelines web site under marine batteries they indicate "provide ample cranking amps for all RV applications, industry leading reserve capacities, two to three times the life-cycles and a virtually non-existent defect rate". Notice they say RV!
Ample Power (the true Geeks of the battery world) actually says that AGM’s are NOT really ready to be used in Deep Cycle Boat applications. After our experience I concur. When our batteries died they didn’t slowly wander off into the sunset, they went south fast leaving little or no warning. Further; after reading Morgan’s Cloud web site where they’ve been working with a Lifeline engineer, they’ve discovered that to keep the Lifeline AGM’s really healthy and to get the most amp hours / dollar out of them, you really need to condition them once / month (in wet celled batteries that’s called Equalize). In addition a posting on the Cruisers Bulletin Board one individual noted that an Optima engineer said that may be best to for their line but it’s not yet the company line and another boat electrician has replaced way too many in the last year. To condition them you need to run the Lifeline batteries up to 15 + volts for 8 hours or 16 volts 6 hours. Then you need to make sure you have copious amounts of ventilation as the by product of this process is Hydrogen (an explosive gas) as the batteries come back to full life. One of the initial pro's for AGM's had been that you DO NOT EQUALIZE! Now the battery manufacture engineers indicate that is a false statement. Further, if you run them flat they won’t come back 100%; again contrary to what was said a few years ago about AGM’s. If we wanted our boat to be a dock queen then AGM’s would be a good option. We don’t want to live at the dock. Now I know there might be a few that have noticed how much time we’ve spent at the dock in the last few years - much too long - but that isn't our goal. I’m sure AGM's are quite good for RVer’s that plug into the power grid on a regular basis but for a boat on the hook they do not make sense. Thus no more Lifeline AGM’s till the charging process is simpler and the recovery from a deeply discharged battery better.
For me, we replaced our house bank with Gels. They've been around longer, have much the same characteristics as AGM's and the critical regulator charging manufactures have the correct charge routines for them. Back in my working days we use to say, "If you live on the cutting edge you end up bleeding"! That's not for me anymore. I'll wait till LIfeline and Optima have it all figured out.
In 2018 we replaced the gels with Lithium and have been quite happy ever since. Lifeline AGM's Grade D