An additional comment on the "run the batteries dead" comment.
You don't want to run them DEAD dead. NiCad and NiMH should NEVER EVER EVER be run deader than 0.95 volts per cell - doing so will do them GREAT HARM, far worse than not discharging them regularly.
If you have a digitally controlled system, odds are it'll shut the light off when the battery gets this low. But if you just have a regular ole' light on a battery, you could run the batteries stone dead, and that will kill them fast.
In fact the whole "memory effect" thing barely has any truth to it anymore. It came about years ago, and the original observations of it were on a satellite that went into earth shadow like clockwork every x minutes and then into sunshine (charging) every x minutes. If you load NiCad like that, discharging them PRECISELY the same amount every time, you can get a noticable memory effect, but it's not that bad anymore; modern NiCads are much better than they were 10+ years ago.
NiMH barely has a memory effect at all. You would probably need a digital voltmeter and a lot of time to detect it. The big nemesis of NiMH is running them too dead, and overtemperature when charging. If you charge a whole pack at a time, be sure to get a charger that has a temperature probe to keep from boiling your batteries.