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Old 05-11-2013, 11:03 PM   #21
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City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
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Originally Posted by Moonstruck View Post
It kinda goes with my philosophy of never passing up a chance to pee, and never trusting a fart.
There's a third one, but I guess in some cases it no longer applies.

ksanders, I agree with you. If you have a batt monitor, the voltage is usually irrelevant and often misleading. On my boat at anchor, I have very little load on the batts throughout the night ...normally just a small GPS and an LED anchor light. For years, all I had to refer to was a voltmeter. Even now, my first action when getting out of bed is to compare house voltage with % SOC. If I saw a great divergence from the table (which I have printed and laminated at my lower helm), I'd know something is going south. My second action is to start the coffee on the inverter!!

I posted the chart to help answer his original question and give an idea of the % SOC voltages at rest. I missed his AGM comment and posted the lead acid voltages which are incorrect for AGM batts.
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Old 05-12-2013, 12:02 AM   #22
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City: SEWARD ALASKA
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Quote:
Originally Posted by FlyWright View Post
There's a third one, but I guess in some cases it no longer applies.

ksanders, I agree with you. If you have a batt monitor, the voltage is usually irrelevant and often misleading. On my boat at anchor, I have very little load on the batts throughout the night ...normally just a small GPS and an LED anchor light. For years, all I had to refer to was a voltmeter. Even now, my first action when getting out of bed is to compare house voltage with % SOC. If I saw a great divergence from the table (which I have printed and laminated at my lower helm), I'd know something is going south. My second action is to start the coffee on the inverter!!

I posted the chart to help answer his original question and give an idea of the % SOC voltages at rest. I missed his AGM comment and posted the lead acid voltages which are incorrect for AGM batts.
You did wonderfully, you just posted what you'd been exposed to.

At most of my jobs over the years I tested high capacity battery banks in Telephone CO's and places like that as part of our Preventative Maintenance. I didn't do it every day, but did do it several times a year over a period of decades. The banks were 48 volt systems. We applied a steady load of generally 100 amps then read the voltages every x number of minutes creating plots of the system. What we found is that under load batteries very quickly (generally within 15 minutes or so) went to exactly 2.0 volts per cell, then stayed there for the duration of our test, which generally ran for an hour, sometimes two.

The big things we checked for were low voltage cells, and high intercell millivolt readings which pointed to high resistance intercell connections (which could lead to fires).
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