I guess you bought a similar cordless tool set to me from B&Q a few years ago. I now have the same problem: good tools but declining batteries. If you open up the battery pack you will find 15 of 1.2v NiCad rechargeable cells all joined in series using soldered tagged connections. It is possible to buy replacement cells, eg from Maplins, but at about £3 each, its cheaper and easier to buy a new drill!
Tim, August 2008
