I've been buying various models of cordless drills since 1990, my first two were 9.6 volt B&D with keyed chucks and metal cases (remember those?) that set me back $120 each. I still have the drills and they work well but replacement batteries are $53 each....
Since then I have gone through Dewalt 12 and 14.4 volt, Skil 14.4 volt, various models of Craftsman 9,6, 13.2, 15.6, and 16.8 volt models, the drills have usually held up well but when the batteries need replacing, you are better off buying a new drill. My all time favorite was the Dewalt 14.4 with the XR pack batteries.
I have never understood how it works....one replacement battery is $50, a new "smart" charger is $60 when purchased separately, yet you can buy the kit with a drill, two batteries, and a case for $100, usually discounted.... /forums/images/graemlins/confused.gif.
There's a website, voltmanbatteries.com, in Ohio, that specializes in remanufacturing cordless tool batteries, but I never visited it...gonna go check it out. They may be out of business now, who knows.