In article ,
"Stupendous Man" wrote:

My in-law knows a lot more than most about electical things. He buys old
devices with bad ni-cads, then charges up a huge capacitor with something
about twice the battery's voltage and zaps it. he says half of them come
back as it toasts the sulfate short-circuits.

I used to do that when my 14.4v NiCads were bad, but they are junk now
so I use 24 vdc (2 car batteries in series) at high current for about 20
seconds. It zaps them enough they will charge normally and hold a
charge for 24 hrs. Within a few days they are back to less than a volt,
but apparently I can re-zap them and recharge when I need to, it does
take a couple of hours to recharge so I have to plan ahead.

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