ni cad batteries

Has anyone here shocked their "dead" batteries back to life like they show on u tube? Ive loads of dead batteries and i cant be throwing away perfectly good cordless tools but on the other hand, cant be spending half the price of a new tool just for a snide rebuilt battery. Ive just bought and sent back two replacement batteries for my sds boschamer . They were made from really cheap plastic for the case and didnt charge although showing 5 lights. I gave one of my old ones a belt from my mig welder and i think it may have revived it. For how long, i dont know. Any views?
Edit, sorry, i thought i was in AG. Ive put it up there aswell.