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Old 10-01-2020, 11:57   #1
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Winter storage battery voltage

My 3 year old Lifeline AGM’s have decreased from 12.6v to 12.1 v in 6 weeks of storage in Maryland.
All loads are turned off, and the current temp is 45 degrees.
Is this normal, or something to worry about?
She is stored on the hard, and electrical power for the charger is difficult.
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Old 10-01-2020, 12:46   #2
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Re: Winter storage battery voltage

That is much faster than self-discharge should be.

Are you sure the batteries are 100% isolated, no monitoring gear attached? An actual fully-isolating bank switch right near the bank is best.

Have you been seeing other evidence they are nearing EoL?

Were they actually at 100% Full SoC 6 weeks ago? How do you usually verify that?

Was the temperature much warmer then?

Can you get some solar onto them?
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Old 10-01-2020, 12:54   #3
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Re: Winter storage battery voltage

When my boat was on the hard last year, I just used one 20 watt panel and a $16.00 PWM controller to keep them at 13.2 volt float during midday. (two 12 volt batteries in parallel)

You could probably get this setup for maybe $50.00 or less and hook it up in 10 minutes
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Old 11-01-2020, 14:13   #4
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Re: Winter storage battery voltage

Quote:
Originally Posted by altinr View Post
My 3 year old Lifeline AGM’s have decreased from 12.6v to 12.1 v in 6 weeks of storage in Maryland.
All loads are turned off, and the current temp is 45 degrees.
Is this normal, or something to worry about?
She is stored on the hard, and electrical power for the charger is difficult.
Not normal, suggests to me all loads are NOT turned off. Look for something less obvious (stereo memory? CO detectors? etc.). Failing finding something like that, disconnect.

When we've stored on the hard with AGMs, self-discharge over 4 months was negligible.

-Chris
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Old 11-01-2020, 15:54   #5
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Re: Winter storage battery voltage

High quality AGM batteries as well as high-quality gel cells will not appreciably self-discharge overdose many months. In one long term test a Fullriver agm sat idle for 6 years and recovered , put back into service and performed well for 3 more years. Also had a Sonnenshein gel cell display similar results. High quality design and manufacturing is what produces very low self discharge.
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Old 11-01-2020, 17:18   #6
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Re: Winter storage battery voltage

Does your bilge pump turn on intermittently?

What kind of electric charge do you use if you had shore power easily accessible?
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Old 16-01-2020, 14:37   #7
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Re: Winter storage battery voltage

Quote:
Originally Posted by altinr View Post
My 3 year old Lifeline AGM’s have decreased from 12.6v to 12.1 v in 6 weeks of storage in Maryland.
Fully charged Lifeline AGMs should be closer 12.9v so at 12.6v the batteries were not fully charged when you left the boat so now they have permanently sulfated and will have lost a lot of capacity. It sounds like your charging regime needs looking at more closely.
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