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Shelgail 07-24-2006 01:55 PM

Equalizing AGM batteries
I have two Lifeline AGM batteries and two West Marine (East Penn) AGM batteries on my IP37. They have not been holding their charge recently. I spoke with the Lifeline people, and they said my batteries should be equalized. When I spoke with the people from East Penn they said that their AGM batteries should never be equalized. Trying to equalize them would make them worse.

Question: Has anyone successfuly equalized their AGM batteries?
If so, a description of your technique would be very helpful.


capn_dave 07-24-2006 02:53 PM

It's not a good idea
AGM's may not go dead very easilly, but if they do, you have to have the capability of "equalizing" them to get them back. When AGM's go dead, they will charge back up under normal charge parameters just like they normally do, slightly faster maybe, but they will not hold that charge. I.E., their true capacity will be greatly diminished. If you find that the batteries reach 13.1 volts and yet as soon as a load is put on them they start dropping down much faster than normal you need equalization. Oh, yes, equalizing a sealed battery is not a good thing to do, but Lifeline will heartilly recommend it as soon as they hear what you have to say the problem is.
15.5V for 3 hours is an AGM's equalization parameter. If you have a newer Link 2000 with an AGM battery selection (#3), then it "may" have this parameter in it. Some do, some don't. If not, set it for Lead Acid (#1) and raise the ambient temp to max... 120? and let it run for 3 hours. That will do 15.75V which is ok. This is of course, AFTER you have charged them normally and they "show" full charge. Now, with the Link 2000 and Heart Inverter/Charger, and access to shore power, this is easy. Since cruisers "often" run batteries dead, accidentally of course, and do not always have access to shore power, you should consider having the capability of putting out that 15.5V off your alternator so you could accomplish this if you needed to away from the dock.

Fair Winds

Cap'n Dave

dave.verry 07-24-2006 03:45 PM

NO! Stop!
NEVER, NEVER, NEVER equalize these batteries against the manufactures advice. AGM batteries are known in the industry as VRLA (valve regulated lead acid). These batteries have a stringent charge requirement to prevent a condition known as thermal runaway at high temperatures and to maintain full charge at low temperatures. Without the proper charger, these batteries have been known to explode. Admittedly, these explosions have happened, as far as I know, only in industrial settings. However, some of those that did where in controlled environments, i.e. air conditioning. Most have happened in huts without adequate air temperature control (ever been in your boat in the sun while it’s in the slip). I have never heard of one happening on a boat, but there is always a first time. I have yet to see a marine charger with temperature compensation (lowering the float or charging voltage at high temperature and raising it at low temperature). They may be out there, if so, if you insist on having AGM batteries or sealed batteries you should invest in one.

Sealed batteries use to be the craze in the early 90s with the maintenance free battery for your car. When is the last time you have seen a new car with a maintenance free battery as standard equipment? Now granted, auto batteries are not deep cycle, but the chemistry is the same.

Replace your batteries. Do NOT try and revive them. I have been designing chargers for the telecommunications industry for over 20 years (mostly VRLA batteries) and will NOT have them on my boat. A good set of wet cells (notice good, i.e. deep cycle, thick plates. Etc.) will outlast VRLA every time if maintained properly.

capn_dave 07-24-2006 05:22 PM

Dave, I agree
However Xantrex makes a charger with temp compensation. What I am not sure of the voltage limits in the equalize mode. The new ones do, the problem being, one wont know unless one has the operating manual.

Regular lead acid wet cell batteries are way better and more bang for the buck.

Fair winds

Cap'n Dave

DynaMeme 07-24-2006 05:51 PM

We installed a commercial marine temperature compensated charger on our last boat in 1998. The present owner just wrote me (among other topics) to say the batteries continue to deliver full performance.

What ever you do in this situation it is a good idea to back up and ask why you are having to do it. AGM batteries are very sensitive to charging regimen. Done properly they will deliver excellent service for 10-15 years. Charged improperly they will fail to deliver even half the expected amp hours.

First, these batteries were designed around three stage charging.
Second, the voltages (and temp comp) for charge, absorb, and float phases are critical.
Third, they must be recharged 100% on every cycle.

That last item is critical. No deep cycle battery should ever be discharged more than 50%. Many people with a wet cell background have become accustomed to considering a battery charged enough at 85% -- about the point reached when the long absorb/float process begins. Wet cells tolerate this reasonably well. AGMs do not.

AGMs treated this way will recover less and less of their performance on each charge cycle. It starts slowly, but within a season or two, a 600amp hour bank can be delivering less than 100 amp hours before reaching a discharged voltage state.

For this reason if the engine hasn't brought the batts back for us when we shut down, the generator is fired up until all the amphours are returned (Via Xantrex).

I recommend Steve D'Antonio's AGM article published in Ocean Navigator for a fuller description.

camaraderie 07-24-2006 11:08 PM

Amen to Dynameme's post...but the problem remainns...what to do about AGM's that have not been holdinng a charge if you don't have a fancy system that has the built in circuitry to do it. I recently read of a "pulse" conditioner that "vibrates" the scale off the battery plates so you don't have to put in an equalizing charge. Any one know about this or have in use experience with one?

dave.verry 07-25-2006 07:55 AM


Excellent post and the advice goes for any battery system you install, wet cells as well as AGM or gel-cells.


Most of the pulse chargers will work for a short time, but they may not address the real problem of VRLA (AGM and gel-cell) batteries. These batteries will tend to dry out when they are cycled too deeply, charged with too high of voltage, kept at a high temperature and charged, i.e. everyday life on a boat. And since they are sealed there is no way to add the water back. As pressure increases within the battery with excessive charging and/or high temperature, the valve (Valve Regulated Lead Acid) will vent the pressure, i.e. hydrogen, to prevent damage (this is the way it’s suppose to work). With the hydrogen vented it’s eliminated from the battery environment and so cannot combine with the oxygen (via a catalyst) within the battery to maintain the water level. Hence, dry batteries, dead batteries.

None of my customers (telecom companies) use a pulse charger. They have tried them and concluded they don’t work. They just replace the batteries after fiver to ten years (and that is on 20 year batteries), more often if they are in harsh environments.

A dead AGM battery is a dead battery and should be replaced.

camaraderie 07-25-2006 09:26 AM

Thanks Dave...guess I'll just have to take care of my AGM's so I don't have these far so good after a year...Time will tell.

hellosailor 07-28-2006 06:46 PM

"15.5V for 3 hours is an AGM's equalization parameter. " I don't know what LifeLine quotes but the AGMs I have from other makers will start to cook and boil off electrolyte WAY BEFORE 15.5V. If you can get them up that high, you will definitely harm them by boiling off electrolyte, even if you don't melt anything internal.

Since there are several different technologies and chemistries being used, and an AGM maker can set the blow-off valve to different pressures, I'd second the recommendation to never exceed the manufacturer's ratings.

Mkfcdl 08-19-2006 11:13 AM

Equalizing with Link 2000
This may be an old topic, but I thought I'd share my equalizing attempts with the Link 2000(R). This is specifically in regards to Lifeline AGMs--which Lifeline says should be equalized at 15.5v x 8 hours as follows:
Charge with voltage-regulated (Constant voltage) charger.

Charge1 @ 15.5 volts for 8 hours.

Avoid overcharging. All batteries must be adequately vented during charging to avoid accumulations of explosive hydrogen gases. Never install or charge in a sealed container or sealed room.

Equalizing should only be done when the battery is showing symptoms of capacity loss or from inadvertent deep discharges. In the event equalization is necessary, make sure to go through the normal charge cycle. Once the battery is fully charged, begin equalizing.
The above is from Lifeline's website. So, I tried to equalize following the Link 2000 instructions. The Link 2000 will keep the voltage at the battery's acceptance level according to the manual. With battery type selected as type 3 (AGM) and normal tempurature setup (80), when in equalization mode the voltage only goes to 14.3 @ 2-4amps (batteries fully charged before trying equalization). This is obviously not a true equalization voltage, so I decided to override the battery setting to Type 0. Now, equalizing sends the voltage to 15.8v at 60amps. Needless to say, I chickened out and immediately shut off the charger.

So, the alternative is "equalizing" in AGM-mode which basically keeps the voltage in acceptance mode (14.3) rather than dropping down to float (13.3) for 8 hours. Will this help a sulfated AGM battery just to keep the voltage at 14.2-14.4? Probably not but if anyone else has done this let me know.

You know, I don't think you have to equalize fuel cells :D .

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