AGM batteries discharged over winter down to 8V or less. Damaged??

[paulg222]

The marina where I leave my boat for the winter has a service where they regularly charge the batteries on board, so I decided to let them do that. They say they normally disconnect the batteries completely in between charging so that it doesn't get drawn down by anything still active.

For my boat for some reason they say they never did that disconnection step. Which is odd since it seems they would have to notice that every time they visit the boat to charge and decide again not to disconnect them. But ok.

Long story short I visit my boat and I'm not getting any voltage read out and no lights will turn on in boat. Batteries are connected and set to All. I normally check voltage using the MPPT charge control display similar to this one . In this case that display was completely off, whereas earlier in the winter I visited the boat and it woke up and showed me the voltage. Note: yes I normally have solar panels but these are removed for the winter for shrink wrapping.

So I told the marina, and they checked it out and said yes, voltage was down, and they said it got down to 8V and they are charging them now.

By the way marina invoice shows multiple visits to charge the batteries over the winter, but were they not checking voltage, or what?

Bottom line: Have my AGM batteries been damaged permanently? What do I do?

Brand of batteries: I just go the boat last year, so I'm not sure, . There are some letters on the top but I can't make them all out and the phrase "...the heart of the " and then I can't make out the rest.

[NBs]

Hi,

doesn't seem good. Does your charger have a separate program to renew the battery, sulfide removal program?

NBs

[Lowcountry]

AGM batteries below 50% charge is not good. I would replace all of them if they were down to 8 volts, they will never be reliable.

[alamoana]

Charge them at a low rate and see what happens…they just might be ok! Good luck

[Statistical]

Seems like the marina owes you a refund for the non-service plus the cost of new batteries.

Your charge controller may have a conditioning setting which could help but very likely the batteries are toast. Even if you eventually do get some useful voltage out of them be sure to capacity test them because you likely have lost 30% to 50%+ of the capacity usable capacity.

This is why boatyards get a bad rep. Nothing like paying someone to destroy your equipment through incompetence. I mean they could have the courtesy to at least destroy your equipment for free.

[CSY Man]

Had the same on my brand new AGMs, after a week in storage I found the voltage at 5.35v.
No idea what happened, maybe 1 battery had an internal failure and dragged the other one down..?
Called Optima, their position is that boat should be plugged in to a battery maintainer at all times.
I got one battery up to 12.68v, the other one only reaches 12.48v.
Figured they got permanent damage, will have the boat dealer sort it out: Boat and batteries was brand new January 2023.

[CharlieJ]

One sure way to destroy an AGM battery is to leave it in a partial state of charge (PSOC) for any period of time. I doubt that you will be able to recover them.

[ranger58sb]

Originally Posted by paulg222

Bottom line: Have my AGM batteries been damaged permanently? What do I do?

There are some letters on the top but I can't make them all out and the phrase "...the heart of the " and then I can't make out the rest.

Looks like they might be Lifeline batteries, which also happens to be the only AGM brand (that I know of) where you can equalize (aka condition) them every so often.

If so, they're good batteries, in general... and they may charge up fine, maybe with only a little damage, and maybe addressable by conditioning.

First, get the the Lifeline manual from their site. Then if necessary, call their tech support guys and ask how best to proceed.

-Chris

[TBW]

An experience I had may at least give you some small "hope".
About 14 years ago I had a new boat. Still have it. Two banks of 6 Lifeline 8D's.
(Victron inverter which turned out to be significant.)
One morning after I had had the boat for maybe 3 months, I went to the boat and everything was dead; 3 volts on the batteries. Lots of trying and checking this and that.
found a little chip in the inverter that was "burnt". Sent the inverter back to victron - in Maine i think - not pleasant people. They repaired the inverter and sent it back. Meantime, I talked to Lifeline. They sent me a special "military grade" charger by overnight Federal Express. No deposit, no charge, just sent it. Then they stayed on the phone with me off and on for 3 days while the batteries were brought back - lots of special charging. Special charging is all I remember. Received the inverter back from Victron. Hooked everything up. A week or so later the same thing. Lifeline sent me the charger again, went through everything again. Batteries back. Advice from Lifeline "Get rid of that Victron Dude". They introduced me to Magnum Energy. Got a Magnum inverter (have several now). Threw the Victron off of the bow in 2000 feet of water (felt good). Lots of "not our fault" from Victron.
Those batteries ended up lasting me nine years. The discharges cost me about a year of life. Oh, I have yet to pay Lifeline a penny for the use of the charger. No FedX charges either way, nothing. They refused all offers of payment. I am about halfway through my second set of Lifelines. All is well.
Call them. They will at least try to help you. Victron will probably yell at you about how nothing is their fault. Use a Magnum inverter.
Good luck

[s/v Jedi]

You have the best AGM batteries that can be bought: Lifeline. They invented AGM batteries.

Unfortunately you ruined them. You may be able to get a little more life out if them by using their equalize procedure as explained by another comment above, but you will never regain the health percentage that they had before this complete discharge.

Don’t delay doing this recharge and equalize.

[smac999]

going down to 8v and then charging right away is probably fine (like same day). getting down to 8v and sitting at 8v is terrible for them. especially if it was weeks.

only way to know is to fully charge them and then do a c20 test.