I have similar issues. I had the entire series of Black and Decker 18 volt NiCd tools, and accumulated quite a pile of free batteries from special deals. As you probably know, the problem with NiCd is low cell voltage (1.2) and so each battery has 15 cells! As soon as one shorts out, then the others begin to get a higher charging voltage and current and quickly also begin to cook while charging, and fail. The slow 9 hour charger was the most kind. The fast chargers are lethal. So I would take the packs apart, and replace the individual shorted cells.... quite a labor of love or stupidity. When lithium came on the scene, I quickly learned that the best deal on batteries was the Lowe's Kobalt 24 volt 2.5 AH which is only $20 !!!! I modified my electric bicycles to use these (I have a youtube video on how to do it) and was quite happy with that idea. Then I thought, why not try the lithium batteries on the B&D tools? The tools work fine.... but I can't any longer pay $35 for a B&D NiCd when I can get the lithium batteries for $20. Of course they dont fit without an adapter. But I had a whole load of dead 18 volt NiCds, each with the charger plug on them, so I just took the batteries apart and used the plate for the adapter. I have several youtube videos on how to do this. Takes a little time and some gorilla glue, and of course the polarity is backwards so beware you have to switch the wires. And the drill goes a little faster on 24 volts, but not a real problem for me.
The 40 bolt lithium tool series from Kobalt is pretty good, and the 5 year no questions asked warranty is insane! As I told the salesman, there is not a chainsaw made that I cannot destroy in a year.... and they warranty it for 5 ??!! So far I have swapped out 3 of them.... the oilers are less than ideal. I am currently trying the Lynx 40 volt chainsaw from Harbor Freight..... it is $20 cheaper, and the warranty only 90 days. But how do I solve the battery compatibility problem? The Lynx battery is $59.... similar to the Lowe's but I have four of the Lowe's ones.