Apologies for the length of this post but I wanted to include what I feel is relevant information.
I have a bank of 3 x BAT412121104 gel batteries on my sail boat, they are linked up to a 12/40 Centaur Charger which is left on while we’re away from the boat. I use a ODELCO DCC 4000 battery monitor to see what the batteries are up to. When the batteries and charger were installed 3 years ago I recalibrated the battery monitor to 390 amp/hours.
When the batteries 2018 were new the battery monitor was reading 376 amp/hours, after a year (2019) this was 378-384 amp/hours but the next year (2020) around 365 amp/hrs. This year (2021) they seemed to deteriorate quickly down to 270 amp/hrs.
One weekend while moored for 48 hours the voltage got down to 12 volts and we had to charge with the engine. While on the mooring we were using about 2 amp hours for the fridge and a bit of led lighting at night. After that episode the batteries were still reading 270 amp/hours after charging.
Last weekend after anchoring for 24 hours the windlass dragged the voltage way down causing the nav instrument to turn off, the engine was running but that didn’t seem to have any impact.
But after recharging the batteries were reading 309 amp/hours and each time they are charged (I turn the charger off overnight due to the constant noise) they seem to gain 10 – 20 amp/hours and when we left the boat were reading 351 amp/hours and 12.77 volts after being off the charger over night. The people who fitted the batteries said it was to be expected that the batteries would loose 30% of their capacity after 3 years, which was a bit disappointing as I was expecting a significantly longer service life than that.
Sorry for the long story but can anyone give me a clue as to what’s going on? Do I need to replace the batteries or have they staged a miraculous recovery?