The HardwareSecrets gang have posted an article that they claim is evertything you need to know about Nickel-Cadmium (NiCd) batteries, including the infamous "memory effect" and how to prevent it. Hrmm... seeing as how I don't know NiCd from NiMH, I think I'll take their word for it....

""Nickel-Cadmium (NiCd) is a very well known rechargeable battery technology, used by several electronic equipments, such as laptop computers, cell phones, cordless phones, old motherboards, etc. It is also very well known by its (in)famous 'memory effect', which makes this kind of battery to lose its charge faster when it is old than when it was brand new."