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Reconditioning batteries - Page 3

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Posted by Piccolo Pete on July 5, 2008, 8:18 pm

Tilt...  God, I've been doing electronics for over thirty years and you guys
make me feel like a total idiot when it comes to batteries.  I'll try
rereading your post a few more times to see if I can get a grip on what you
are saying.

Thanks for the info though.


Posted by Eric Sears on July 9, 2008, 12:16 pm

I've been watching this thread to see what this comment came to - re
the reverse charging.

A comment and then two real life "i done 'ems".

Re the matter of "blowing up chargers" - of course if you stick one on
a low resistance battery - ie very flat (but not too sulphated), or
reversed - well the current will likely kill the charger - that's why
you would use current limiting like a bulb in series with the charger.

About 15 years ago, my son "rescued" some old flat 12v,6ah gell
batteries, found by a rail depot. One had "claim" written on it. They
all (about 6 of them I think) measured between about 2v and 6v as I
remember. Trying to charge them resulted in less than about 1mA (much
less I think) in the "charging" direction. They appeared very
sulphated, with 1000's of ohms impedance.
Then I discovered that with a reverse charge voltage, the current very
gradually increased. I watched it carefully until it reached a maximum
and began to decrease again, then reversed the charge again. After a
while (you had to watch it carefully!!) the charging current would
begin to kind of "pulse" up and down, and then begin to run away. Out
of about 6 batteries, I was able to restore 3 of them to some
semblance of working order. In fact I still USE two of them today.
they will still light a 12v,25watt bulb with dropping below 12v under
load, for some while. I use them with electronic circuits - as power
supplies, when experimenting. They are probably about 20 years old

Second, much more recent example.

About 8 years ago I was given a brand new 80ah, 12v deep cycle
battery. I would call it an "ersatz" deep cycle - it looked like a car
This year I was about to throw it on the lead scrap heap, as it would
take no appreciable charge at all - even after charging for a good
number of days. Note - it had had very little use over the intervening
years, though it had got "left" without regular charging at times.
Then I tried the reverse charge trick. Again, it began with a small
current, which gradually rose, and I monitored the voltage across it
(falling) until it just reached zero volts. I then reversed it again.
After some playing with forward and reverse charging, it now seems to
hold about 40ah, and lights a 60 watt bulb for a good number of hours.

Ok guysand gals - have you tried it?
It doesn't seem to work with all states of batteries (definitely not
shorted cells!), and sometimes they have not recovered. The critical
thing seems to be the point at which the "reversing" takes place.
I don't fully understand the "right" way it might be done - but I DO
now have a useful battery in place of a piece of scrap.

Eric Sears.

Posted by Ron Rosenfeld on July 5, 2008, 11:24 am

Depending on what shape they are in, you might be able to improve them by a
controlled overcharge, or possibly with a desulfator.  Just be careful to
monitor the water level and the temperatures during this process.  If there
is no mfg recommendation, my advice would be to make sure the cell
temperatures stay below about 110F or so.

Some have found that several weeks of "equalization" might be required

But, if you are going to just add these batteries to your existing system,
you should be aware that mixing batteries is not generally recommended.
You'll probably wind up with a bank that reflects the worst cell condition.


Posted by Piccolo Pete on July 5, 2008, 1:27 pm

Certainly not.  I would switch the line when one bank is low.


Posted by Ulysses on July 5, 2008, 4:32 pm


I have had *some* luck with the Desulfate setting on my charger, but it's
not a miracle worker or anything.  I suggest running the Desulfate four or
five times before trying the Equalize setting.  The Desuflate uses little
power so it won't overtax your system (probably).  17 volts was mentioned--I
think that is way too high.  It should probaly be more like 15.5 volts for
equalization.  If your battery continues to draw high current after being
charged for a long period of time and it feels too warm my experience says
it's wasted and you would just be wasting a lot of power trying to restore
it.  Ron says 110F.  Maybe stick a thermometer in the cells?

I think the Desuflate setting can be helpful if used occasionally on
batteries that otheriwise are in good condition.  Equalization should be
done as routine maintenance on good batteries every four-six weeks or so.

Another trick I have used with a battery with a couple of weak cells is to
remove and save the electrolyte from the good cells, remove some electrolyte
from bad cells, put the good electrolyte in the bad cells and distilled
water in the good cells in an attempt to get the cells more even.  It works
sometimes.  You don't end up with a good battery but you might end up with
one that is still usable to some extent.

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