I think the silence gives a clue. You probably can't!
There are specialist outfits that will re-cell battery packs and some people have posted on here about their attempts / successes but it's probably not worth it for a DIY grade tool. Problems include the high price of NiCd cells and soldering contacts that are normally spot-welded.
Mostly, tool manufacturers offer a drill with its battery at an attractive price, but make a replacement battery expensive, so you are more likely to replace the whole thing. Not environmentally desirable.
There was a post somewhere about just keeping the drill but using a 12v car battery charger instead of a 14.4v battery. You could try that; or you might strike lucky on eBay, Freecycle etc.
Apart from that, I find that the old Brace and Bit is cheap and reliable!!
Just a thought...I have 2 B&D drills, 12v and 7.2v. I have used a DeWalt charger on the batteries, 12v no problem, but on the 7.2, I think I had tear off a small lug on the battery, but it did charge-I don't have the original charger for this drill. Rick.
i recently needed to replace my Bosch drill battery, as its a few years old and having been left in shed with hot and cold weather over the years, the battery cells had it.
I looked on ebay and they were stupid prices, the drill was around £90 new and the replacement batteries are not far off, but it was a 24V and althought i can pick up a cheap 18V replacement, i that it was daft to throw away a perfectly good drill/driver.
I actually opted to buy all the new battery cells and take out the old (20x1.2V). All you need is patience, soldering iron and a hot glue gun, oh, yest photograph the old battery. Its relatively simple, postitive goes to negative and all long as you put it back as it came out (photo every thing). He presto, you have a replacement battery, relatively cheap.
old nicads can be rejuvinated, have a look on utube, people zap them with a mig welder to burn off the dendrites. Not tried it myself but if its knackered already what have you to lose. If you are replacing the batteries I'd go for NiMH they don't suffer the dendrite problem it is possible to bring wires outsire and use a different batterypack. Could be charged with any variable power supply or even car battery charger.