You need to “zap” them. Essentially what this means is supplying about 10 to 12 amps of current for a VERY short period of time, less then 1 second. You must also open the pack and zap each cell, observing the correct polarity for each cell. I have seen many circuits that will do this for you; most involve charging a large capacitor to about 12 volts and then dumping it across the cell. Do a search on the net and you will find some of these circuits. I do it manually using a 10-amp 12-volt power supply. After each zap, check the voltage across the cell with a meter, if you have 1.25 or more volts the cell should be ok. If you do not get 1.25 volts, zap it again. Be VERY careful, you are dumping a lot of energy into the cell and it will get warm. I would not zap it more then about 3 times and then let it cool for a while. After about 5 zaps, it is probably not going to work. Sometimes you cannot resurrect a cell but most of the time you can. After you get all the cells in the pack to 1.25 volts or more, charge the pack as you normally would, then use it down and charge it again. Remember, the best thing you can do with/for nicads is use them often and hard.