NiCad batteries need to be discharged periodically to prevent the memory effect and prolong their lifespan.
Batteries such as NiCad, Lead Acid, and NiMH contain TOXIC chemicals. Techniques should be taken to prolong their lifespan, and when you do discard them, they should be recycled, not thrown in the trash.
One technology to watch is the Iron battery. Such a battery could reduce some of the toxic waste problems associated with used batteries, however such a battery is probably a few years away.
Some remarks about backlights in laptops, monitors (screensavers), harddisks (hdparm), etc. have to be written.