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6v 5AH SLA AGM battery dead but being revived possibly?
6v 5AH SLA AGM battery dead but being revived possibly?
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Old 22nd May 2019, 01:24 PM   #1
realflow100 is offline realflow100  United States
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Default 6v 5AH SLA AGM battery dead but being revived possibly?

I have it hooked up with two 150ohm resistors in parallel to a 12v battery to give it enough voltage to start pushing a charge into it.
at first it was only drawing like 1 or 2 mA of current and the voltage across it was close to 12v
after 15 minutes it quickly started dropping down to 11.5v and then 30 minutes later it dropped quicker down to 10v and an hour or so later it's now at 7.5v and still dropping but its dropping slower now. and its holding voltage better too
when i first got it it was at like 2.5v at resting voltage now its holding closer to 5v at rest and drawing close to 100mA of current. and the voltage is still dropping slowly as it maybe gets more charge?
can it be saved? it came out of a kids powerwheels car thing
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Old 22nd May 2019, 01:27 PM   #2
pelanj is offline pelanj  Czech Republic
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If the battery was below 4 V for more than a day, the electrodes are most probably already sulphated beyond usable and you will save your nerves by buying a new accumulator.
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Old 22nd May 2019, 01:29 PM   #3
Mooly is offline Mooly  United Kingdom
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6v 5AH SLA AGM battery dead but being revived possibly?
When a battery of this type is left discharged it can suffer from sulphation of the plates and that may not be recoverable.

The official Yuasa guidelines are to charge at higher voltage and with the current limited to one tenth the battery's capacity. That voltage could be as high as 16 to 20 volts but the current in your case must not exceed 0.5 amps. There is also a time limit of 12 hours.

The battery should also not be left unattended whilst doing this.
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Old 22nd May 2019, 01:40 PM   #4
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina
If the battery is sulfated, there exists in the web a thing called "desulfator", a guy I know tried it in a battery from a car and he affirms that it works. I'm skeptic about it, but as it is easy to build, perhaps you can try it.

desulfator circuit - Google Search
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Argentine Ham Radio LW1DSE since 1987.

Last edited by Osvaldo de Banfield; 22nd May 2019 at 01:42 PM.
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Old 22nd May 2019, 01:48 PM   #5
realflow100 is offline realflow100  United States
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i am constantly monitoring the battery
but im charging it with 12v and current limited to 50 to 100mA
and right now its slowly increasing current as it starts to take a charge. so the voltage is dropping slowly while charging. but the resting voltage when not charging is increasing
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Old 22nd May 2019, 02:06 PM   #6
Mooly is offline Mooly  United Kingdom
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6v 5AH SLA AGM battery dead but being revived possibly?
12 volts isn't enough to charge even a new battery.
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Old 22nd May 2019, 02:08 PM   #7
realflow100 is offline realflow100  United States
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its a 6v battery. not a 12v battery. i even wrote in the title 6v 5AH battery
not 12v.
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Old 22nd May 2019, 02:11 PM   #8
Mooly is offline Mooly  United Kingdom
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6v 5AH SLA AGM battery dead but being revived possibly?
I don't know why I didn't spot that, sorry

So your 12 volts is OK and you can increase the charge rate up to 0.5 amp to try and recover the battery. Make sure it doesn't start to overheat though, if it does stop the process and let it cool down.
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Old 22nd May 2019, 02:23 PM   #9
realflow100 is offline realflow100  United States
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i cant increase it that much. i'd need more than 12v and i dont want it to build up a lot of gasses or boil the battery.
right now its at about 6.9v and still slowly dropping in voltage but the current is still slowly increasing. i'm going to leave it on for a while before i try to charge it at more current. its still not charged enough to charge it normally. need to get the internal resistance low enough that it can take a normal charge current.
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Old 22nd May 2019, 02:39 PM   #10
realflow100 is offline realflow100  United States
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ok the resting voltage is just about 5.4v i hooked it up to my normal battery charger set to 3 cells 6v pb/lead acid mode and current set to 100mA and its almost to the point where it can take a normal charge. the voltage went up to 7.35v but its internal resistance is decreasing further. its dropped down to 7.2v after a minute or two of being on charge.
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