This comes from the web, generously submitted by those mor
knowledgeable than yours truly on the subject. Use at your own risk.
good smart charger seems to be the best answer to all of this, alon
with keeping things cool. Nothing lasts forever, and it is not wort
getting burned or losing an eye over a battery. Of course, nobody like
to be ripped off.
Case in point: Bosch sells two types of chargers, a smart charger and
standard charger. They include the standard with thier drills, you ca
buy the smart for about 50 bucks. The smart supposedly increase
battery life by a factor of four. If they are interested in th
environment, why dont they just include the smart charger with th
drill? Cost of parts? not hardly. They want to sell batteries. That
where they make the real moola. why do you think inkjet printers are s
Before doing any of this, consider what your time is worth. Most of u
boomers do this because we come from a world where things could b
repaired. That world is gone.
Zapping NiCds to Clear Shorted Cells
Nickel-Cadmium batteries that have shorted cells can sometimes b
rejuvenated - at least temporarily - by a procedure affectionatel
The cause of these bad NiCd cells is the formation of conductiv
filaments called whiskers or dendrites that pierce the separator an
short the positive and negative electrodes of the cell. The result i
either a cell that will not take a charge at all or which sel
discharges in a very short time. A high current pulse can sometime
vaporize the filament and clear the short.
The result may be reliable particularly if the battery is unde
constant charge (float service) and/or is never discharged fully. Sinc
there are still holes in the separator, repeated shorts are quite likel
especially if the battery is discharged fully which seems to promot
I have used zapping with long term reliability (with the restriction
identified above) on NiCds for shavers, Dustbusters, portable phones
WARNING: There is some danger in the following procedures as heat i
generated. The cell may explode! Take appropriate precautions and don'
overdo it. If the first few attempts do not work, dump the battery pack
Attempt zapping at your own risk!!!
You will need a DC power supply and a large capacitor - one of thos
70,000 uF 40 V types used for filtering in multimegawatt geek typ
automotive audio systems, for example. A smaller capacitor can be trie
Alternatively, a you can use a 50 to 100 A 5 volt power supply tha
doesn't mind (or is protected against) being overloaded or shorted.
Some people recommend the use of a car battery for NiCd zapping. DO NO
be tempted - there is nearly unlimited current available and you coul
end with a disaster including the possible destruction of that battery
your NiCd, you, and anything else that is in the vicinity.
OK, you have read the warnings: READ THE WARNINGS, DAMMIT!
Remove the battery pack from the equipment. Gain access to the shorte
cell(s) by removing the outer covering or case of the battery pack an
test the individual cells with a multimeter. Since you likely trie
charging the pack, the good cells will be around 1.2 V and the shorte
cells will be exactly 0 V. You must perform the zapping directly acros
each shorted cell for best results.
Connect a pair of heavy duty clip leads - #12 wire would be fine
directly across the first shorted cell. Clip your multimeter across th
cell as well to monitor the operation. Put it on a high enough scal
such that the full voltage of your power supply or capacitor won'
cause any damage to the multimeter.
Wear your eye protection!!!
Using the large capacitor:
Charge the capacitor from a current limited 12-24 V DC power supply.
Momentarily touch the leads connected across the shorted cell to th
charged capacitor, + to +, - to -. CAUTION: Polarity is critical - d
it backwards and you will make the problem worse, probably terminal
There will be sparks. The voltage on the cell may spike to a high valu
- up to the charged voltage level on the capacitor. The capacitor will
discharge almost instantly.
Using the high current power supply:
Turn on the supply.
Momentarily touch the leads connected across the shorted cell to the
power supply output, + to +, - to -. CAUTION: Polarity is critical - do
it backwards and you will make the problem worse, probably terminal.
There will be sparks. DO NOT maintain contact for more than a couple of
seconds. The NiCd may get warm! While the power supply is connected, the
voltage on the cell may rise to anywhere up to the supply voltage.
Now check the voltage on the (hopefully previously) shorted cell.
If the dendrites have blown, the voltage on the cell should have jumped
to anywhere from a few hundred millivolts to the normal 1 V of a charged
NiCd cell. If there is no change or if the voltage almost immediately
decays back to zero, you can try zapping couple more times but beyond
this is probably not productive.
If the voltage has increased and is relatively stable, immediately
continue charging the repaired cell at the maximum SAFE rate specified
for the battery pack. Note: if the other cells of the battery pack are
fully charged as is likely if you had attempted to charge the pack,
don't put the entire pack on high current charge as this will damage
the other cells through overcharging.
One easy way is to use your power supply with a current limiting
resistor connected just to the cell you just zapped. A 1/4 C rate
should be safe and effective but avoid overcharging. Then trickle
charge at the 1/10 C rate for several hours. (C here is the amp-hour
capacity of the cell. Therefore, a 1/10 C rate for a 600 mA NiCd is 50
This works better on small cells like AAs than on C or D cells since
the zapping current requirement is lower. Also, it seems to be more
difficult to reliably restore the quick charge type battery packs in
portable tools and laptop computers that have developed shorted cells
(though there are some success stories).
My experience has been that if you then maintain the battery pack in
float service (on a trickle charger) and/or make sure it never
discharges completely, there is a good chance it will last. However,
allow the bad cells to discharge to near 0 volts and those mischievous
dendrites will make their may through the separator again and short out
And this one from Tom Lamb:
Measuring NiCd capacity - I use a very simple/effective system. Put a
2.5 ohm resistor across the contacts of a cheap travel analog clock,
which will time the rundown. It is quite consistent for good cells. A
good typical AA NiCd will run one hour.
NiCd zapping - I use a 1 ohm power resistor in series with a car
battery, though a series headlight will also work. I charge for about
30 secs or until warm, which will clear the whisker and put in enough
charge to see if the cell is salvageable.