I have two banks, one a starting battery which is just a car battery
which has only been used once, the other a "house" bank of two Group 31s
that are used for everything. They are connected by a combiner so the
house set can't run down unless I change the A/B switch to include it.

I have only been getting two years out of the house set but switched
over to a "Battery Minder" which is supposed to desulfate them when I
leave it on them all winter. It only gets down to -35 up here in
Minnesota; I haven't lost a battery yet.

I will report on their progress next spring when I try to run
refrigeration, anchor and house lights and fans a for three days without
charging.

Capt. jeff