[AT] Batteries charged backwards.

[Ken Knierim]

I've got a battery in my Blazer that had been sitting and was completely
dead; it was relatively new before I parked it for several years. It would
not take a charge so I purposely charged it backwards, bled it dead with a
resistive load (light bulb), charged it with correct polarity and put it
back in service. It's been starting and running the truck fine in daily
service for about 4 months so far. I don't hope it'll be perfect but it's
nice to get whatever life I can out of it at this point.

Your mileage will vary. I've had successes and failures with this method
but it sometimes works.

Ken in AZ

On Wed, Feb 12, 2020 at 3:28 AM Stephen Offiler <soffiler at gmail.com> wrote:

> 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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