Are we talking about 'discarding' them or 'recycling' them ? I doubt there is anything left to 'recycle' or reclaim in them. It is OK to discard them. It is common sense to discharge them completely, first. I use the NiCad discharge function on the charger - mine takes them down to 0 volts, at 5 amps. I do this several times, then twist the power leads together and tape them to the side of the battery. They swell up pretty fat. Then I let it cool completely and drive a nail through it, and throw it in the trash. This method was described on RC Groups several years ago and I have never seen any updates to it. There was some method that used salt water bath, but it was found that the tabs corroded off before the battery was completely discharged.