Battery voltage drop overnight

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2 months 1 day ago #6233 by PirateHulagirl
Battery voltage drop overnight was created by PirateHulagirl
We are trying to figure out if we should purchase new AGMs for our boat (IP350 #4). Our current system (one Gp24 and 4 Gp27) give us about 460 Ah but they are six years old. While on the hook we start our night at around 12.65 and by morning we sometimes might be as low as 11.99. All we have on is our fridge and anchor light.

My questions: Is this normal or would new batteries hold their charge much better than what we are seeing? Is it realistic to think I could spend two nights at anchor and not have worry about running the engine to recharge given my current setup?

Thanks for any input.

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2 months 1 day ago - 2 months 22 hours ago #6234 by TheCuscus
Replied by TheCuscus on topic Battery voltage drop overnight
Hi. My guess is you'd use about 50 amp hours in the overnight. 12.65 is about 75% charge, 11.99 is fully discharged. So if 50 amps takes you from 75% to zero, I'd say your batteries are done. How do you charge them? AGM's require a specific charging regimen to stay healthy. With that said, 6 years isn't too bad.
Check this site for very good battery/charging info
marinehowto.com/
Last edit: 2 months 22 hours ago by hayden.

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2 months 1 day ago #6235 by PirateHulagirl
Replied by PirateHulagirl on topic Battery voltage drop overnight
TheCuscus, thanks for replying so quickly. So we have a one solar panel (135 watt) while on the hook and we also have a wind generator. But we don't use that unless we have substantial wind. I believe the batteries need to be replaced but really want the advice from other IP owners. And like you said, six years is not too bad. If/when we replace them, we are going to go to Gp31's. That will give us around 525 Ah vs the 460 we have now.

Thanks again man.

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2 months 1 day ago #6236 by Delicia
Replied by Delicia on topic Battery voltage drop overnight
I agree, that you likely need new batteries, But I would add a bit of caution. If it is warm and your box has not been reinsulated you may lose 65 amp hrs over night at anchor - that is what our 350 did at 80 degrees before I reinsulated it. Also, if you have a conventional anchor light rather than an LED you will use about 1.6 amps * 12 hours? = 19.2 amp hrs Plus the panel at .6 amps another 7 amp hrs, and a water tank gauge light at .7 amps another 8.4 amp hrs. So all together perhaps around 100 amps hrs +or-. This is about a 25% of your bank. 12.06 volts is 50% discharged.

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2 months 1 day ago #6237 by PirateHulagirl
Replied by PirateHulagirl on topic Battery voltage drop overnight
Delicia, thanks for the detailed information. So with new batteries holding a charge better than what we are getting now, what would be a reasonable number to see on our charger when we wake up in the morning? Something North of 12.3 ish?

Thanks again for such quick replies. We are ready to make a purchase ($$$) and get ready to have some fun.

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2 months 1 day ago #6239 by TheCuscus
Replied by TheCuscus on topic Battery voltage drop overnight
FYI, AGM battery voltage as state of charge (SOC)
12.80+ 100%
12.60 75%
12.30 50%
12.00 25%
11.80 0

The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life.

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2 months 22 hours ago #6240 by hayden
Replied by hayden on topic Battery voltage drop overnight
Scott:

Have you ever equalized this battery bank? That being, applying 15.4v to the fully charged bank for 2,3,4 hours? Sometimes this will revive older batteries. I equalize my AGM battery bank every year. It makes them act as new again.

Also, like DELICIA said, you need to insulate the frig. My frig runs at 50% of the time, so 6 amps x 12 hr = 72 amp hrs in 24 hrs. My battery bank is 525 amp hrs, so 262 amp hrs usable. We have 450 watts solar on a Solar Boost Blue Sky controller that is fantastic and we have 450 watts of wind which is great in 10 knots+ We use 100 to 125 amp hrs in 24 hrs. Our solar will make 75-80 amp hrs and if we have wind, we are full all the time.

So, I would #1, look into an equalization charge, sometimes called a conditioning charge, if that does not fix it, then I would buy new AGM Lifeline batteries.

PS:
Gp 31 will fit where Gp27 fit, same size, but the Gp31 xl at slightly bigger. Check it.

Hayden

Hayden Cochran
IP35-165 Island Spirit
IslandSpirit35.blogspot.com
Rock Hall, MD

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