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Old 15-12-2013, 09:44   #1
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AGM SOC Voltages Chart?

I have searched the internet and this forum, in an attempt to understand my battery bank state of charge, to find a chart that correlates the percent left in an AGM battery to voltage. There seems to be some variation in these charts.
So, anyone recommend a chart that they have confidence in?
Thanks
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Old 15-12-2013, 10:09   #2
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Re: AGM SOC Voltages Chart?

The voltage level at different SOC will vary by AGM manufacturer. A Lifeline AGM will not be the same as Rolls AGM. So you should use one from your particular brand and model. Using voltage for SOC is not that accurate. You need to disconnect any loads and let the batteries sit for awhile after charging to get a meaningful value. Not something that is that easy to do on a cruising boat.
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Old 15-12-2013, 12:51   #3
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Re: AGM SOC Voltages Chart?

Quote:
Originally Posted by Paul L View Post
..........You need to disconnect any loads and let the batteries sit for awhile after charging to get a meaningful value. Not something that is that easy to do on a cruising boat.
It is easy - just disconnect one battery and let it sit for about 5 hours. Next time you do the test disconnect a different one.

Also remember that the voltage at each SoC will be lower as the batteries age.
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Old 15-12-2013, 13:59   #4
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Re: AGM SOC Voltages Chart?

agree that manufacturers seem to have different ideas about soc. i have flooded batteries. both trojan and interstate have soc charts and they're both different.

i've been using voltage as a way of checking soc for many years now and i think i've gotten as much life out of my batteries as anyone else. sometimes i measure specific gravity, but you can't do that with agm's. you don't need to know the EXACT state of charge, just keep it in a high range. i doubt that most cruiser ever get near 100% soc.

here's the trojan guide, which includes an soc table...

http://www.trojanbattery.com/pdf/TRJ...UsersGuide.pdf
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Old 15-12-2013, 14:24   #5
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Re: AGM SOC Voltages Chart?

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Originally Posted by gbanker View Post
I have searched the internet and this forum, in an attempt to understand my battery bank state of charge, to find a chart that correlates the percent left in an AGM battery to voltage.
It varies between manufacturers.

We're using Lifeline AGMs because Senta had ~10-year old Lifeline AGMs which were still functional when we bought her so we replaced them with identical new ones.

The image below is a screensnap of the Lifeline manual showing SOC vs. Voltage. I think another thing to remember is that the SOC is presumably relative to the current battery capacity which decreases over time.



-Sven
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