Lessons in the care and feeding of AGM batteries

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Ned

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Four years ago, I replaced my four OEM T-105 batteries with 4 Lifeline GPL-4C AGM batteries.  AGM batteries promised longer life, quicker recharging and all around better performance.  In fact, they performed as expected for several years, charging quicker than the flooded cell batteries, and giving excellent performance.  Last January, one of the batteries failed and was replaced by Lifeline, prorated for a 5 year warranty, and everything worked fine.  This fall, I had indications of another failed battery and a load test showed that one of the now 4 year old batteries had indeed failed.  One of the others showed marginal performanace under load.  The symptoms I saw were my inverter shutting down after about an hour of use with a ~40A load on the batteries.  At that load, they should have gone at least 3-4 hours without needing charging.

I have spent some time on the phone with a tech from Lifeline and he asked how I used my batteries.  I told him, that like many of us, we spend most of our time on shore power with the Heart charger on to keep the batteries charged, and several months on the road with shore power at night.  We boondock about 3-4 weeks a year, typically, where we get good use from the batteries.  The tech said that with that kind of use I could expect about 4 years of useful life, which is just what I had experienced.  He said that rather than keeping the charger on when on shore power, the batteries should be given a rest when not being used and this will then give the expected useful life of up to 10 years.

When I bought the batteries, all the information I could find said that AGM batteries were not to be equalized.  The tech said that isn't the case, and the Lifeline web site AGM user guide also says that equalization can be done when the batteries show signs of lost capacity.  Since that's what I was seeing, I ran an equalization cycle on the batteries and they no longer showed the catastrophic voltage drop I had seen before (the voltage would drop from ~12.2V to 10.2V almost instantly after about an hour under load) but they did drop to 75% discharged (11.75V) in a little over an hour.

So I have ordered 3 new GPL-4C batteries to add to the one replaced last January.  1 will be prorated under the warranty and the other 2 will be full price.  I will now be turning off my charger until the batteries show they need charging and just let my 48W solar panel trickle charge them most of the time.
 

Ned

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Joined
Feb 1, 2005
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Nope, they lasted about 4 years, and were dying.  I think part of the problem is the AGM batteries require a lower float charge voltage than flooded cell batteries.  I tried to compensate for that by upping the ambient temperature setting on the charger, but I think the float voltage was still too high.  I think I'll replace my Link 1000 with a newer version that has a specific setting for AGM batteries, but I'm going to contact Xantrex first and ask.  Meanwhile, I'll keep the charger off most of the time.
 

blueblood

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Mar 16, 2005
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Ned said:
.

When I bought the batteries, all the information I could find said that AGM batteries were not to be equalized.? The tech said that isn't the case, and the Lifeline web site AGM user guide also says that equalization can be done when the batteries show signs of lost capacity.?


FWIW- When I talked to a member of Lifeline family DAVID GODBER before I bought mine, he stated that because of typical usage of RVer recharging batteries frequently (i.e. connecting to shore power all most every day) thus minor discharge levels rather than heavy discharge levels like a boat user ,who is off shore power for a long stretch, their batteries should never require equalization when applied to RV's.?
 

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