Selkie was in indoor cold storage over the winter in northern Michigan and I had no access to her. The storage contract provided that the batteries would be disconnected and that trickle charges were not permitted and only staff could run chargers. We heard from the yard that the 2 year old AGM batteries are not accepting a charge.
We questioned the yard about its failure to monitor battery status or charge them and this was the reply, in part:
"We have found and backed by battery manufactures specs that if a AGM battery is good when all loads are unhooked they can sit dormant for six months without going bad or needing charged. "
I have owned cruising boats for 50 years and have never left a battery without attention over winter storage. And I know that Lifeline-the premium US AGM manufacturer calls for battery maintenance during winter storage.
In CT, I disconnect neg post during the part of the winter the boat is on the hard and too cold to work on.
When things warm up, I’m down at least once a week and I run an extension cord to top off the batteries. I’m replacing 8 yo carbon mat batteries this season with run of the mill AGM.
Hoping for 4-5 years with the possibility of a re-power when they need replacing. Maybe electric propulsion.
I was able to recover my batteries after an unintentional discharge/damage incident using a very inexpensive smart charger. You can read about it here and see if it applies to your situation.
I’ve had good success with a small solar panel. Around 50 watts, no controller, just hook it up and walk away for a week or two.
If the batteries are completely discharged there was a draw on them over the winter. Definitely disconnect the negative terminal from all batteries when in storage.
According to the Lifeline tech I talked to, if the batteries are sulphated from over discharging, it takes a high voltage/current to knock it off of the plates. This is how the repair mode on some smart chargers works and the one I tried seemed to work well. My batteries would not take a charge no matter how long I tried with a regular charger. They came up within a few hours with the smart charger. Not guaranteed to work, but worth a try, since the charger only cost something like $80.
Seconding @Vela33 's experience with this. My batteries got deeply discharged over the winter due to unintended neglect. I have a NOCO Genius battery charger which recovered them after about 8 hours, and they are performing at least ok. We will see how well they hold a charge when I move from the dock to my mooring in a few weeks.
Don, Have you had a chance to examine the batteries? Assuming there are at least two, it’s unlikely that both would fail. I would check to make sure the connections to the charger are tight. Do you have 12 V batteries connected in parallel with one charger or is it a smart charger with separate +/- leads to each battery. A new charging unit might be in order. If the batteries were truly disconnected then there would be no phantom discharge except if they were defective and they would hold a charge over the winter. I think they lose something like 2% per month. Worst case is to contact the manufacturer for warranty replacement.
Won’t have access to the boat for a couple of weeks. Three house batteries in parallel, plus separate start. Unclear if the yard used on board charger or their own. On board is smart charger with two 15 amp leads: one to the house bank in parallel and the second to house.
Got a charger from Amazon and will try to equalize/repair batteries individually.
Don, Have you had a chance to examine the batteries? Assuming there are at least two, it’s unlikely that both would fail. I would check to make sure the connections to the charger are tight. Do you have 12 V batteries connected in parallel with one charger or is it a smart charger with separate +/- leads to each battery. A new charging unit might be in order. If the batteries were truly disconnected then there would be no phantom discharge except if they were defective and they would hold a charge over the winter. I think they lose something like 2% per month. Worst case is to contact the manufacturer for warranty replacement.
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