Occasionally I encounter a NiCad cell which has gone short-ciruit.......

The standard cure is to use a set of car jumper leads to briefly zap the
crook battery across your car battery.
(in the "charging" direction.....)

This will certainly remove the short, but please be aware that if you manage
to stick the leads to the battery, the resultant explosion will be somewhat
interesting.....

My experience is that the "cure" is seldom permanent. Once a NiCad becomes
flakey it is best to discard it......

............................ Zim

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