How to rebuild Ni-Cad battery pack for power tools
What should I replace them with? I've wired up battery packs for RC cars and stuff before, and I'm confident I can put it back together properly. The problem is I'm having a hard time finding the nicad cells now. did they stop making them? I see a few for sale and they're like $3-5 per cell now (I need like 50 of them).


Nickel-Cadmium (NiCd) cells are falling out of favor, because Cadmium is environmentally unfriendly and usually not compliant with RoHS.  Nickel-metal hydride (NiMH) are replacing NiCd.  NiMH and NiCd have similar characteristics (more thorough comparison of NiMH and NiCd here).

You can buy both NiCd and NiMH cells from industrial electronics distributors.  Here, for example.


  Is it possible to salvage the good cells from several different dead ni-cad packs to create one working battery?


It depends on the actual packs and how you're planning to charge.  In a general case, I wouldn't mix and match used cells of unknown pedigree.  It wouldn't produce the best results, probably.  I would buy a uniform batch of new cells.

p.s.  Of course, when you say "power tools battery pack", most folks knows what you're talking about.  However, a photo of your tool's battery pack would help this question a lot, especially if you've already disassembled it.  Please post it if you can.