I've done the same thing with a 12 volt car battery.
"+" to "+" and "-" to "-". make contact very briefly, just enough to
maybe spark.
Brings them back to life for a while.

Dave

wrote:

I've had good luck clearing NiCad batteries that short out internally.
This is mostly caused by age or overcharging among other things.

Use a large electrolytic capacitor (maybe 5000 microfarad or so) &
after you got the polarities right, dump it into the bad NiCad cell.
Smaller caps need to be charged to a higher voltage, but the concept
is to get a major current surge into the bad cell.

What happens to NiCads as I understand is there forms a metal whisker
between the foils that prevents the charging current from charging
that particular cell. Each cell is 1.2V so you can evealuate a
battery pack by seeing if the output voltage is N*1.2 where N is the
number of cells.

If not, the entire pack can be treated to the "shock" effect although
it will require a higher charge voltage on the electrolytic cap.

What the heck - it junk otherwise isn't it?

I have not had similar luck with lead acids of course, or NiM hydrids
etc however.

I wouldn't casually switch batteries without getting the right charger
unless you know what you are doing.