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.
One more thing to watch:
Do you use the NiCD battery to power an altimeter?
If yes, keep in mind that a NiCD 9V battery has some 8V only, fully charged. Not all altimeters will like that.
Further NiCD's do have a very low internal resistance. This means that they can supply plenty of amps on a shorted igniter. Not all altimeters do have output circuits that can handle this current, some will get damaged if ever the igniter gets shorted.
NiMH are much better: No memory effect and their internal resistance is comparable to alkaline batteries.