On 21 May 2005 20:14:08 -0700 wrote:

Is it possible to resurrect a lead acid battery from the dead?

I have an old 12 volt automobile battery that was stored for
sometime in a discharged state. The battery voltage read around
6 volts in the discharged state. I charged it at 1 amp for 10 hours and
then tested the capacity using a automotive tail light drawing 1.3
amps. The battery voltage fell from 12.5 volts to around 9 volts within
1.5 hours indicating the capacity was not too much.

The fact that it got to 12.5V indicates that it is probably not
shorted internally. Charge it up again and leave it overnight. If it
still measures above 12V then it is likely to be restorable.

Open up the cell caps and look down each one with a flashlight. You
should see the plates with paper separators between them. The paper
will be tan colored and I'm guessing that you'll see grey plates
between each tan separator. If so, your best bet is to charge the
battery extremely slowly.

I recommend that you just put a small lamp between the charger and the
battery, in series, to limit the current. A charging current of about
50 mA is about right. You will need to keep this up until half of the
plates turn chocolate brown. At that point, the battery will be fully
charged. If your battery is badly sulfated, this process may take more
than a week.

During that time you should check the voltage across the battery. You
can do this at the same time that you're charging it slowly. If the
battery voltage every falls below 12V during this time, you have a
shorted cell, and the battery is probably not salvagable.

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Jim Adney
Madison, WI 53711 USA
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