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?

 

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.

 

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.

 

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.

 

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.

 

@crutschow What voltage would you recommend? How much capacitance?

 

@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.

 

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.

 

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.

 

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.

 

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.