12V 5Ah AGM battery charging question (sulfation issue???)

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,128
Been holding 13.8 V on a 12V 5Ah AGM battery. Been on for a week at that voltage. Immediately upon disconnection from the power source the battery voltage reads 11.88 V. When charging current (if we can call it that) is 5 mA. This battery is probably beyond recovery. Question - is there a way to make the battery draw more current without putting the battery, charger - or the house in danger?
 

Chris65536

Joined Nov 11, 2019
164
I do remember you could supposedly fix dead NiCads by "zapping" them with high voltage & current, but I have never heard of fixing a dead lead-acid this way. These seem to die like clockwork. If there's a way to fix them, I'd love to know! We have 14 UPS's at work and they get new gell-cell batteries every 5 years. At least they're 100% recycled.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,128
This battery came out of a battery powered tire pump. It's been regularly charged for a few years, but it has sat on the shelf for over a year - neglected. I've heard of possibilities of recovering this sort of battery - but that's YouTube, and I don't readily accept what I see there. I've seen too many false postings, also too many people who don't know what they're talking about to trust what is being presented.
 

crutschow

Joined Mar 14, 2008
24,306
Sounds like you have a shorted/bad cell, not sulfation.

You could try one of those "zapping" techniques using a large capacitor.
I don't have a lot of confidence that will work, but it couldn't hurt.
 

nsaspook

Joined Aug 27, 2009
6,894
Sounds like you have a shorted/bad cell, not sulfation.

You could try one of those "zapping" techniques using a large capacitor.
I don't have a lot of confidence that will work, but it couldn't hurt.
Exactly.

A shorted cell with the rest being over-volted/charged (drying out the electrolyte) until they die from the charging energy
Time to Recycle that battery.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,128
@nsaspook - You're probably right. But if it's easy, why not try and recover it?! It's not an expensive battery, but it IS a battery after all. Well, only if it's good.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,128
Tried pushing the voltage up to 14.9 volts. Upon disconnection - the battery voltage seemed to drop off to 11.6V. Lower than I started with. Maybe that's necessary - maybe it's beyond recovery.
 

nsaspook

Joined Aug 27, 2009
6,894
Tried pushing the voltage up to 14.9 volts. Upon disconnection - the battery voltage seemed to drop off to 11.6V. Lower than I started with. Maybe that's necessary - maybe it's beyond recovery.
You're risking Sudden Unscheduled Disassembly if you keep pushing voltage into a 'dead' battery without good current limiting.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
4,128
You're risking Sudden Unscheduled Disassembly if you keep pushing voltage into a 'dead' battery without good current limiting.
LOL! Yeah, I worry about that sort of issue. Sudden Unscheduled Disassembly Syndrome (SUDS) makes me nervous. Don't worry, I already disconnected the power source. And no, I didn't stop to check the current. Fool that I can be at times.

No battery swelling or bulging and no "Baby Rattle" when shaken. Cells are not dry. I've seen that before, an overcharged battery that has gone dry internally.
 

nsaspook

Joined Aug 27, 2009
6,894
LOL! Yeah, I worry about that sort of issue. Sudden Unscheduled Disassembly Syndrome (SUDS) makes me nervous. Don't worry, I already disconnected the power source. And no, I didn't stop to check the current. Fool that I can be at times.

No battery swelling or bulging and no "Baby Rattle" when shaken. Cells are not dry. I've seen that before, an overcharged battery that has gone dry internally.
It's an AGM type battery so it's pretty dry even when new and AGM batteries are very sensitive to overcharging. Just one overcharge that causes major h20 electrolysis can kill them.
 
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