Does anyone know how to rejuvenate a NiCad battery? I have several 1.2V
cells in an old cordless drill that I want to bring back to life. I
remember something about 20 years ago that you can zap it with about 70
volts reverse polarity. I can't seem to find anything on the internet about
it. Anyone know? Thanks.
The standard rumor is to put each cell across a 12V car battery for a
few seconds. The idea is to blast away any zinc dendrite (crystalline
fingers) that are shorting the cell. I've done this a few times with
lousy success.
http://www.slams.freeserve.co.uk/Q&A/NiCad FAQ.htm#NICDBATTERY_022
Do *NOT* do it reverse polarity or more than one cell at a time. It's
positive to positive and negative to negative, one cell at a time. If
it explodes in your face, please let me know and I'll apologize.
Another method that only works with if you're really desperate. I've
noticed that some NiCd's die an early death due to electrolyte loss.
The cells are overcharged for various reasons, outgas when
overheated[1], and KOH (potassium hydroxide) electrolyte is lost. So,
my bright idea was to notch the edge of the cell with a triangular
file, and use a syringe to refill the cell with KOH. Batting average
was about 30% which basically made it a wasted exercise.
Cordless drills are not known for using the best quality NiCad cells.
Methinks you're not going to have much luck. If it happens to be a
Makita battery, there are plenty of online vendors with rebuilds and
clones for reasonable prices.
Also, be sure to recycle your old NiCad batteries. Cadmium is a
rather nasty pollutant.
[1] Nicads only get hot when overcharged. You can charge a nicad at
almost any rate you can deliver, without any overheating, as long as
the cell does not overcharge. I've charged 625ma-hr AA nicads at
about 12C rate (7Amps) and gotten a 90% full charge in about 5 minutes
with zero temperature rise. However, I've also exploded cells that
were even slightly overcharged at this rate. Be careful.