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Old 17-09-2019, 11:38   #1
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Charging a sulphated battery

My house bank is pooched. (two 74ah AGMs, two years new). It looks like they were undercharged (charger was set for FLA rather than AGM but the real difference based on the manual is whether the boost or bulk Voltage is applied (14.4V. The Float voltage was 13.8V vs 13.6V).

Before installing new batteries, I wanted to verify the charger was operating properly. I suppose I should have done it with new batteries, but I performed the test with the old bad batteries.

I ran the batteries down to 50% (actually they dropped very quickly past 50%) and turned the charger on. The voltage immediately read 13.6V which is the float voltage and not the bulk (14.4V).

Is it possible that the batteries in their state, could not accept any more current and therefore the charger automatically switched to float voltage?
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Old 17-09-2019, 11:53   #2
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Re: Charging a sulphated battery

What charger do you have? And what size?
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Old 17-09-2019, 11:55   #3
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Re: Charging a sulphated battery

Cristec 40A charger.
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Old 17-09-2019, 12:19   #4
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Re: Charging a sulphated battery

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I ran the batteries down to 50% (actually they dropped very quickly past 50%) and turned the charger on. The voltage immediately read 13.6V which is the float voltage and not the bulk (14.4V).

It will take time for the voltage to get to 14.4V during bulk charging. If the batteries jump quickly to 14.4V from 50% SoC this is a good indication they are sulfated.

A typical Lifeline AGM battery, charged from 50% SoC at 20% of rated Ah capacity in charge current, (.2C charge rate)will take approx 75 minutes to get to 14.4V....
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Old 17-09-2019, 16:30   #5
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Charging a sulphated battery

The 13.6 may have been coincidental, I know thatís float, but it could also be the voltage where the charger maxed out. if the charger was maxed out at 13.6 then it is, if itís not putting out its full amperage, itís either bad or the batteries are likely badly sulphated.
Although if they were down to 12V or close to it and jumped immediately to 13.6, thatís not likely a good sign.
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Old 17-09-2019, 16:35   #6
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Re: Charging a sulphated battery

Thanks everyone. Is there a better way to test whether the charger is indeed following a 3-stage charge profile?
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Old 17-09-2019, 17:00   #7
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Re: Charging a sulphated battery

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Thanks everyone. Is there a better way to test whether the charger is indeed following a 3-stage charge profile?



Other than connecting to a known good battery?
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Old 17-09-2019, 17:09   #8
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Re: Charging a sulphated battery

Screw the frickin three stage profile. You need to hit them with 14 something for a while. That's get's everything going and then you can see what you have.
I used to sell batteries to small plane owners. They would use the plane twice per year and the battery would dead in 3 years. Sometimes I put the battery on a good charger, boil the **** out of it and it would be good for another 6 months.
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Old 17-09-2019, 17:21   #9
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Re: Charging a sulphated battery

Newer car battery chargers will automatically go into recovery mode to desulphate a heavily discharged battery. Borrow one and hook it to just one of your batteries. The Optima battery website mentions that to get their batteries charged when heavily discharged below the turn-on voltage of a battery charger... hook in parallel to a known good battery, and hook the charger to the good battery.
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Old 18-09-2019, 08:56   #10
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Re: Charging a sulphated battery

Oh yes, smart chargers that will not charge a dead battery, the engineering department should all be fired!
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Old 18-09-2019, 09:16   #11
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Re: Charging a sulphated battery

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Oh yes, smart chargers that will not charge a dead battery, the engineering department should all be fired!

It's actually a safety feature to avoid thermal runaway. The charger has no way to know a battery is internally shorted or just over discharged.
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Old 18-09-2019, 09:42   #12
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Re: Charging a sulphated battery

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Oh yes, smart chargers that will not charge a dead battery, the engineering department should all be fired!


Just crank the engine and the alternator will bring it up enough so the charger will kick in.
I have sort of the opposite problem, that is the Solar will often bring bank voltage up enough so that the Magnum inverter I have wonít go into bulk mode, but goes straight to float, cause 13 V is a fully charged battery, right.
I can trick the magnum by setting the recharge voltage high, so there is a work around.
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Old 18-09-2019, 11:10   #13
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Re: Charging a sulphated battery

Skylark has five Optima Yellow Top AGM Series 31 batteries. In the past 10 years, there have been three instances where the house bank went completely flat.

Learning that desulfating techiques for other styles of batteries don't work on spiral wound AGMs, research led me to purchase a BatteryMinder charger that uses pulsating frequencies to dislodge the sulfate from the "plates".

In the end, I got 10 years out of the three house bank batteries and the two identical batteries that are used on the engine start/windlass circuit are still working and don't seem to want to be replaced at all.

I've been considering switching to Firefly's carbon foam batteries, but when I consider what I got out of the Optimas and what the Fireflies cost, I have to think about it all.
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Old 18-09-2019, 12:35   #14
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Re: Charging a sulphated battery

I recommend that you take them to your local battery supply center, specializing in just batteries, and have them test the batteries to see if they can be equalized. Usually costs about $10 at Battery Warehouse and takes overnight.
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Old 18-09-2019, 13:05   #15
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Re: Charging a sulphated battery

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Just crank the engine and the alternator will bring it up enough so the charger will kick in.
Not if you have a smart regulator on your alternator.
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