What Mike said. Your term "old drill battery" is likely to be the problem, and could've caused the charger to fail. NICD cells generally fail shorted when left sitting around for months at a time, then only charged when needed.
Charging batteries with chargers intended for different battery chemistries is a bad idea. NICD and NIMH tool battery packs don't charge safely or properly by the same methods used for car lead/acid batteries.
And I knew a guy that was so cheap he'd "recharge" non-rechargeable batteries with a car battery, claiming that it worked perfectly, good as new (just a quick zap with a jumper wire). He could've lost his eyes for less than a couple bucks for new batteries.
In some tool battery packs, the T terminal is the (-) charging terminal connected thru a self-resetting thermal protector. Many packs use different methods.
There are many ways to approach power tool battery needs.. some companies specialize in rebuilding packs with higher capacity cells. Empty used pack cases are available on eBay, which can be "good as new" or better, when refilled with fresh new cells. Universal NICD-NIMH, original OEM and other suitable chargers are also available on eBag and elsewhere.
The best quality cells, IMO, are made in Japan.. Sanyo, Panasonic and FDK are some examples. IME, new NIMH cells perform better after the first 6 or so uses, so their performance is considerably better than it seems for the first couple of uses.
By buying new cells with tabs attached, they're ready to be connected safely without soldering directly on the cells.. overheating will typically damage cells and likely cause leaking.