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Old 30-04-2023, 11:11   #1
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1 of 4 house AGMs only charging up to 48%?

Prepping my boat for the spring launch from winter storage on the hard, I had run my 4 AGM batteries down to <5% due to using lights, winches, etc... I then connected a shore power to recharge the house batteries back up to full. Three of the batteries charged up quickly to 100% but after 3 days of charging, one of the 4 AGM's seems to only get to a 48% charge. Engine and windlass batteries topped off to 100% also. The boat and batteries are only 2 years old.
Note: I'm running a 110v/15a extension chord power line split (both sides hot) adapter into the 50amp boat power. I'm not in the water so I can't run the engine/alternator for power or my 50a line.

Any quick thoughts? Is this perhaps a bad battery or might this issue be rectified when I'm back on a full 50 power line or running engine?
Thanks so much!
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Old 30-04-2023, 11:30   #2
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Re: 1 of 4 house AGMs only charging up to 48%?

my first instinct is that the battery is no longer functional and I would replace. Battery life expectancy is dependent on many things and although two years isn't great, given that you essentially drained it to zero charge, it just may not come back. I have no real experience however.
I do know that in my airplane where a battery is critical, I changed them every three years like clock work. Recently I charted a Cat in the Caribbean and the Generator battery was three years old, I was the first charter of the season and I was irritated when it died. My irritation was that it should have been retired at the beginning of the charter season, and not have the charter company wait until it failed.
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Old 30-04-2023, 11:57   #3
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Re: 1 of 4 house AGMs only charging up to 48%?

how are you determining a single battery in a bank of 4 is at a certain % ?
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Old 30-04-2023, 12:06   #4
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Re: 1 of 4 house AGMs only charging up to 48%?

If you have Lifeline AGM's, I believe they are the only AGM with a stated equalization cycle. I have brought them back from near dead to working through equalization, but no guarantees. Dropping to 5% is very far down. I've also found that the "smart chargers" with equalization cycles are actually rather dumb. I use a research grade power supply and run my own cycle using the manufacturers recommendations for conditions.

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Old 30-04-2023, 12:48   #5
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Re: 1 of 4 house AGMs only charging up to 48%?

Since you specify that the problem is with only one of four I assume youíve charged them all separately and they are currently not paralleled? If thatís the case and 3 of them will take and hold a charge but the fourth one wonít Im afraid that means itíll need to be replaced and itís not going to heal itself when the source of power changes after launch. As dlj suggests, you need to be able to periodically equalize Lifeline AGMs and many battery chargers donít do a great job of that. So, like he suggests, I bought an adjustable power supply so I can set it at 15.5 volts and adjust from there based on battery temperature to get just what Lifeline guidelines call for. I think mine only cost around $100 and doesnít take up much room. During equalization at 15.5V, itís only putting out about 4A into an 840Ah house bank so nothing too violent going on but if itís quiet and you listen carefully you can hear the AGM batteries bubbling inside. Batteries need to be fully charged prior to equalization though.
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Old 30-04-2023, 14:58   #6
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Re: 1 of 4 house AGMs only charging up to 48%?

Thanks, folks. I appreciate your responses -very helpful.
I think I need to seek out direction from the dealer on direction (the boat is still under warranty).
I'm not sure if the four batteries are in parallel.
The nav station monitor shows the battery display and shows each of the four batteries charge percentage, amps and voltage.
I'll circle back with an update once I get more detail.
Thanks again.
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Old 01-05-2023, 08:31   #7
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Re: 1 of 4 house AGMs only charging up to 48%?

I would be shocked if the warranty covers battery.
personally, I would buy a new one and replace. The faster you get
it done the faster you are back in business
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