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Old 27-07-2008, 09:31   #1
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AGM low voltage

My AGM's 8yrs old (4 Lifeline 105 amp hrs. each) will not maintain voltage over 24hrs at anchor. The voltage drops to under 11.05 volts within 24 hrs. but the amp hrs. are still above 300 . We are running minimal power at anchor just rerig and one (1) reading light. Needles to say when voltage gets to low it will not run/start some motors and the gen. or motor has to be fires up. Are the batteries done for and need to be replaced or can they be rejuvinated??? Need ideas please!
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Old 27-07-2008, 10:01   #2
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Lifelines are nice I had 2 group 4's on the last boat and they were great. Now that yours are 8 years old they may be slightly rejuvenated unless the pattern of use and charging was not optimal. If all that was poor they would not even be where they are at now. Using an equalization charge there may be something more left but I doubt it's much.

Here is the link from concord

Lifeline Batteries - Marine & RV Deep Cycle Batteries

The biggest demise is not getting them fully recharged every time you discharge them. It's almost impossible to do this on the hook since the last 10% of capacity takes so blessed long.
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Old 27-07-2008, 10:06   #3
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Your batteries sound like they are ready for the scrap heap. You should be keeping them fully charged and they should be holding that charge and not dropping down to 11.8. This sounds like dead completely sulfated batteries.
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Old 27-07-2008, 17:45   #4
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It always cracks me up to read that batteries need to be charged up to 100% after any discharge, especially AGMs.
I doubt that happens much in the cruising life.
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Old 28-07-2008, 03:07   #5
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Quote:
Originally Posted by trt7704 View Post
My AGM's 8yrs old (4 Lifeline 105 amp hrs. each) will not maintain voltage over 24hrs at anchor. The voltage drops to under 11.05 volts within 24 hrs. but the amp hrs. are still above 300...
As previously noted, an 8-year useful life isn’t bad for batteries that have been “rode hard & put away wet”. Sulfation of Batteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4 (12v Battery).

Since an open circuit voltage of much less than 12.20V (S.G. 1.190) generally indicates a functionally discharged battery (in your case about 200 A/Hr remaining), I wonder if your Battery Monitor needs calibrating?

Sometimes, a deep discharge, followed by a slow charge will recover lost Battery capacity and charge acceptance.
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Old 29-07-2008, 01:16   #6
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Plus to add to the great advise by the others, how is the 300Ahrs being measured. If it is a simple add/subtract meter, it will only be calculating the Ahrs via giving you a sum of A x Hrs being put into the bank. It doesn't actually mean that many Amps are being stored in the bank.
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