The thing about a welder is it is CURRENT limited, and won't punch out more than the dial says. Any method using a battery or a capacitor bank, unless you use a resistor too is fraught with dangers. Steve
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I have had luck ZAPPING nicad batteries back to life using 2 methods. Both methods are somewhat DANGEROUS... so try it at your OWN RISK... 1. charge up a large capacitor to a couple hundred volts... then quickly place this charged capacitor across the dead battery..ZAP!!! now put battery back into charger and it will charge up again! (notes: Do this using a PRE-BUILT test jig housed in an insulated plastic BOX. for safety. Flip the toggle switch ONE WAY to charge the capacitor then the OTHER way to zap the battery. 200 volts can KILL YOU so dont mess around with this if you dont know how to build it. 2.. Attach clips to the battery PLUS and MINUS. Then quickly touch the PLUS to a car battery PLUS and the MINUS to a car battery minus (just for a second touch battery terminal. WEAR GLOVES !!! because THIS IS DANGEROUS TOO!!! if the battery is shorted then your WIRES may INSTANTLY VAPORIZE or turn CHERRY RED in your hand.... If that doesnt happen, .. you might ZAP your nicad battery so it will accept a charge again. If you dont end up at a hospital or a MORGUE, you might get your batteries ZAPPED back to life. The reason these methods work, is because nicad batteries develop an INTERNAL short that is blown away by the quick jolt of high current electricity. NEVER NEVER attempt to do this to ANY kind of button cell battery. They will EXPLODE INSTANTLY ! It is a good idea to wear safety goggles when attempting these methods. IMPORTANT : never zap any battery that is still attached to any electronic device... you will damage the device! If under age 18, be sure to get parents to help you. everyone else, attempt at your own risk.
You could try putting 2 or 3 car batteries in series and use that. You could try zapping them with camera flash high voltage like the example on the right under "RELATED". If tried several ways and have NEVER had any luck bring back nicad batteries. But, I maintain my batteries as I use them and I may be actually be just using mine to death. Good luck.
+1 Same with me. I have never had this method revive a single NiCad battery. Burnt some holes in couple of them though.