>> - this isn't like trying to charge a dead, stone cold
>> Lead-Acid cell ...

> Aren't dead Pb batteries dead forever ? I've always been led to
> believe that significant sulphate formation is irreversible, and
> leaving Pb batteries discharged for any length of time is unwise

People doing home power in the US (alternative energy, like solar)
claim 4 out of 5 lead-acid batteries die because of sulfation of
the plates and are recoverable.  Without minimum daily exercise,
the plates will sulfate (gradual crystalization of electrolyte
solution; reduces electrical potential and increases resistance).

Historic technique to desulfate a battery was to force overcharge
every so often.  This wastes energy (which solar/wind/etc people
don't like).  And, when trying to revive a heavily desulfated
battery can easily overheat it (damaging the battery, usually
with a bulged case).

There's a battery desulfator technique using "ringing" of the
electrolyte & plates at the resonant frequency of the battery
(circa 3.6MHz for 12V car battery).  Circuit to do so was
published in Home Power magazine #77, June/July 2001, see:

    www.humboldt1.com/~michael.welch/desulfator.pdf

The "ringing" causes the crystalized sulfate to redisolve from
the plates into the electrolyte solution.  This can take a few
weeks to a couple months using the desulfator circuit and a
trickle charger.

I'm starting some experimentation now on reviving a couple of
car batteries.

Besides the home brew route, there are kits and commercial units.

References include various patents which can be found via IBM's
patent server.

                                                Lee Jones

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