Originally Posted by Randyonr3
Our batteries have.never been on a shore charge. We opperate off of two 130 watt panels
atop our bimini
and a 4-winds charger. And of corse the motor
which has a 140 amp alt from cruising direct with a smart charge regularter... When re building systems in the boat, we opted to spend more for cost effective systems. Our reffer is a good example as we opted to spend more and installed the "cool blue" from technotics. All lighting
is diode including running lights and our water
heater is on demand propane
Every couple months, we shut down each battery individual to let the battery settle and surface charge drop. On the last inspection
(shutdown)-all batteries read between 12.7 and 12.8..
Ah, that is different information than your original post. Most certainly your batteries have seen voltages below 12.6V while operating.
I don't think you have the data to say they are at 90% of original capacity. Even mostly consumed batteries will charge up and give high resting voltages. Actually, I think for AGMs, the resting voltage should be higher than you see since the self-discharge rate is so low.
The proof of the pudding is how long they will sustain a discharge, not how high the resting voltage is.
With 8 batteries and low daily draw, it is very likely that your batteries have lost
considerable capacity in the past 10yrs, but even at this much lower capacity they still fulfill your power needs.
You would need to do a proper load test or run-down test to determine actual capacity left.
I truly do hope they are still at 90% and you get another 10yrs out of them. But that would be against all odds and if forced to make a wager, I would bet against them.