h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Wrap your tired NiCad in a plastic bag and stick it in the freezer overnight, charge as normal and you should be amazed.

I've heard about freezing nicads before and you are right; it's supposed to refresh them. Another tip for people with access to simple electrical bits and pieces..

..wire a simple circuit: small headlamp bulb to a nicad connector. When your nicads won't operate your piece of electrical equipment disconnect them and hook them up to your simple circuit. This will squeeze the last juice out of the nicads and run 'em properly flat so that you don't get the dreaded memory effect.

Trickle charging is also much kinder to ni-cads. Rapid charging tends to "cook" ni-cads and promotes the memory effect as rapid charging doesn't give such a consistent "fill"; most domestic quality chargers are not very stable and fluctations in the domestic mains power supply add to this problem. Trickle charging may take 12-14hrs but you will get many more cycles of life from your nicads.