Several things about NiCd batteries (which is why I switched to NiMH...)
Sandman is right, they have memory. Store them *near* dead. When using them, always DEPLETE them to *near* zero. This is the best way to keep them young and healthy. If you continually recharge them after only using (for example) 25% of their life, they will adopt that as their normal characteristic and will be dead after 25% of their *normal* charge expectancy.
Now, you may have noticed that I emphasized several times "*near* zero"... This is important.
NiCd batteries are dumb (if that even makes sense... LOL). If you draing them to ZERO, stone-cold dead, they *can* reverse themselves. It's a real trip and a real fireworks show the first time you discover this...
never drain them completely to avoid this issue. It is rare, but it does happen. And when it does you will waste a good $20+ battery pack as well as the equipment it is in. I toasted a $200 R/C car this way once. Never again...
NiMH batteries have none of these characteristics.