Should I rebuild or just replace worn out cordless tool batteries?
Rebuilding NiCd battery cell packs can be a good alternative to buying new packs. There are really only a few manufactures of these  type of cells, but the quality can differ as the prices may indicate. The majority of the price of a new pack is the pack package itself, which is specific to each tool, even though the cells inside are pretty similar. The amp hour rating and number of recharges it will take are the most important thing.  I have noticed that the Porter Cable battery packs are a lot less expensive than most of the other brands. To be honest, I haven't researched the brand of cells they use as an OEM, but you can get info online about cell manufacturers and ratings on the quality levels. I would look closely at the warranty the rebuilder is offering, which cells they are using and avoid a bargain basement price with a poor warranty or hidden costs such as a "recycling fee". A supper low price on a rebuild or a complete replacement may indicate a clearance of old stock. NiCd's hate to sit around for long periods uncharged, which can really affect performance and charging ability. Check the date codes and don't accept any that may be much over 6 to 9 months old.