[AT] Batteries charged backwards.

[Stephen Offiler]

I wouldn't get my hopes up, Cecil, but I know you want to give it a try.
They're out of a tractor, you say, so I'm assuming they aren't deep-cycle.
That's not good news - I have had little luck bringing back *any* starting
battery (non deep cycle in other words) that has been completely discharged
flat.  Add the reversed chemistry on top of that and the chances get
worse.

But, go for it.  Kill them dead again.  Keep something hooked to them for a
while longer.  Difference between 6V and 12V bulbs is that the 6V will draw
more current, so it will be faster.  If the 12V is handier, just use it,
and leave it on there longer.  It's not as if the 6V will bring any greater
chance of success.

Best way to bring them up again is to keep the recharge current fairly
low.  Most of my experience is much smaller batteries (think small
motorcycles and power equipment) and I use a lab-grade constant-current
power supply.  (You won't need that)  I go with 1/10 of the A-hr rating of
the battery until I've got 2.2v per cell (I do both 6V and 12V this way, so
that's a handy number to remember) and then go from constant current to
constant voltage for a couple more days.

Group 31 is ballpark 100 A-hr, so 1/10 of that is 10 amps, and I assume
you've got a charger laying around of about this size.

SO




On Tue, Feb 11, 2020 at 9:31 PM Cecil Bearden <crbearden at copper.net> wrote:

>
> > I had 2 group 31 batteries out of the tractor that were completely
> > dead.  I hooked them up in series and connected my 24Vcharger to them
> > as It was handy and I wanted to charge both.  After a couple of days I
> > checked them and found that I had hooked the charger backwards.  I
> > hooked a couple of incandescent headlights to drain the battery, but
> > after 3 days they won't light up the headlights, but they still have a
> > lot of spark when shorted with cables..  A guy at my battery shop said
> > I should hook up a 6volt light to them and use that to run them
> > down....  At $100/ea, I need to try to save these...
> > Cecil
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