Reviving Gel Cell/SLA batteries

[BushmanLA]

My father in law scored a handful of Automotive jump start units, they were free because something was wrong with them and that something is the battery apparently.

They have a honking huge 12V 18Ah SLA battery in them but the two I have show something like 1 volt each. :(

I assume these guys are sulfated all to heck. Anyone got any quick and easy tricks I can try out before I give up on them?

I read that if you trickle charge them for a long time you can dissolve the sulfate crystals. Or you can buy a nice fancy expensive de-sulfator gadget, but I really don't want to do that.

[tadawson]

My father in law scored a handful of Automotive jump start units, they were free because something was wrong with them and that something is the battery apparently.

They have a honking huge 12V 18Ah SLA battery in them but the two I have show something like 1 volt each. :(

I assume these guys are sulfated all to heck. Anyone got any quick and easy tricks I can try out before I give up on them?

I read that if you trickle charge them for a long time you can dissolve the sulfate crystals. Or you can buy a nice fancy expensive de-sulfator gadget, but I really don't want to do that.

If they get too old, the cells corrode and collapse internally, and short out. Once that happens, it's game over, nothing you can do but replace them. Good news is that 12V 18AH is not that big or uncommon, so you should be able to get replacements pretty easily and cheaply if you should so desire. You might also look to see if the batts are swollen - that is a pretty clear indicator of dead beyond repair . . .

- Tim

[BushmanLA]

Is there any way to tell the difference between shorted cells and sulfated cells?

If I apply 12V to them there is no current going in after a second or so, as soon as I remove the external 12V the battery drops to about 4 volts.

[tomahawkflier]

I have a de-sulphator.

If you are showing very low voltages then you should dump the battery. For a 12 volt SLA I would hope to see 10 volts. If less than 10 volts then a de-sulphator won't work

[tadawson]

Is there any way to tell the difference between shorted cells and sulfated cells?

If I apply 12V to them there is no current going in after a second or so, as soon as I remove the external 12V the battery drops to about 4 volts.

IIRC, sulphation reduces capacity, not voltage. So, doing what you are doing with your charger tells me that only two cells are still alive (2V per cell) and the rest shorted, resulting in the low voltage. So, I also vote dump it - it appears to be dead.

- Tim

[jeffs555]

I just revived a marine starting battery that was exhibiting the same symptoms. It had been sitting discharged(stereo turned on) and unused for a year and the voltage read 1v when I started. I first tried a trickle charger for about a week, and it did nothing. A old 5amp charger rapidly dropped to zero charging current and didn't charge either. I read up on the electronic desulfinators and it said they apply high voltage pulses at random intervals. Had nothing to lose, so I used a 24v 8amp transformer with bridge rectifier. I hooked a voltmeter to the battery and connected the 24v. The voltage started climbing and only took a few seconds to get to 15 volts. I shut it off when it got to 15 volts, and the voltage dropped rapidly to about 4v. I did it over and over at random intervals until the off voltage only dropped to around 11 volts. I then charged it overnight with a normal charger and it seems to be working fine. I have had shorted cells before and like the others said there is nothing you can do about them, but this battery was at 1v and no shorted cells. Guess I just got lucky.

PS If you use a 12v dumb charger (ie transformer and rectifier) a shorted cell will cause it to draw excessive current. A sulfated cell will cause high internal resistance and draw low or no current.