Here I am again, singing the same tune...
In 2018 I bought 8 Crown "deep cycle" group 31s. They were great for about a year, then slowly began to deteriorate. With 520 AHr and fully solar charged by early afternoon, when new I was waking up to 25.4-25.6v after about 50AHr use overnight. This slowly deteriorated until I was running the generator before bed to avoid dropping voltage below 24.7. I nursed them along until July 21 and bought 8 NAPA (Penn)105 AHr group 31s. They have already failed, after working great initially, in just 5 months.
I charge at 28.5v Abs, 27v Float, and equalize at 31v (on recommendation of Crown engineer). I have a 105A Magnum charger/inverter, and 850W solar in 3 pairs, each pair with it's own Victron MPPP controller, and a 60 A alternator using a Balmar external regulator.
My first 3 sets of similar hybrid batteries didn't start to deteriorate until they were 30-36 months old. This started after I installed solar. Watching the voltages and solar output closely shows them acting as they are set to act. Measuring amperage at the primary 25v cable from battery studs to switch, I don't find any excess current flowing with switches on or off. All batteries measure within 0.1v after disconnecting for 6 hours. All cells have SG 1.019 +/- .001, which does not improve after 6 hrs equalizing at 31v. All read within .2v of each other after load testing, which shows them barely in the "fair" range. It doesn't seem to be a matter of one bad battery or cell, or unequal charging...they are all deteriorating at the same rate.
I need new batteries again, and am thinking about AGM golf cart batteries. So far they are all 11.5" height, and my very early SM2000 has only 10.5" battery box height. I'm also only able to install 8+1 group31 batteries, limiting my total AHr capacity.
I'd like to make the switch to LiFePO4, but insurance is proving to be a problem. I had hoped by the time my current batteries failed I'd be able to find insurance...alas, they've gone belly up after only a few months.
I'd love to hear any thoughts about my current ( no pun intended) problem, 6v AGMs that will fit my space, Lithium conversion insurance availability (I'm US flagged, but could register elsewhere, I guess).
Kent & Iris