I am a former Sears tool associate. This could be one of two very different problems. Either the charger is bad and needs replaced or you have a bad battery. If you are getting a partial charge with a shortened battery life, then the nicad battery most likely hase developed a "memory." This usually happens when a partially discharged battery is recharged or stored away in a partially discharged state. To prvent the memory, it is always best to completel discharge the battery before recharging or storing. Case in point, I have a Craftsman 19.2 combo kit with 7 year old batteries and an 11 year old Dewalt 12v drill. All the battery packs still hold a great charge.
If you are getting no charge at all, then you probably should replace the charger itself. Best way to test is if you have afriend with the same size battery that you know works, try charging that on the charger. If it charges a known good battery then you have a problem with the battery. If not, then it is the charger. Hope this helps.