Rejuvenating Batteries

Don't remember the actual post but would be very interested to know myself. In the mean time try this link on battery rejuvenation. May be of some help.

Cheers Mick

What type of batteries are you talking about?
I'll assume you're talking about cordless power tools.

Theres a few reasons why their batteries don't last - they are usually garbage (look at how cheap they are) - the chargers they come with are primitive, so they can both overcharge and undercharge - and many power tool owners don't know how to look after their batteries.

If it is running NiCad cells, then yes you can rejuvenate.
NiCad cells like to be fully cycled every time they are used. If you run them to near flat, let them cool, and then recharge them to 100% you will get better capacity and more voltage out of your packs. To slip them onto the recharger when they are not fully discharged is not good.

If you cycle them several times, as you suggest, then you can return some capacity to a poorly maintained battery. Easiest way to discharge is to run the drill until it starts to slow. Best voltage to drop the pack to is 0.9V per cell (or 3/4 of the pack's total voltage), but you've probably got no way of measuring voltage. If you run the drill until it's stone cold dead, you will also damage the pack as current gets reversed in the weakest cell in the pack, so eventually that cell will die.

NiMH cells also like to be cycled, but are more tolerant to partial discharge, so they have largely replaced NiCad. They are also a bit more friendly to the environment. You may get a bit more capacity by cycling a NiMH a few times, but the effect is not usually as great as with NiCads.

The above is info gained from matching NiCad and NiMH cells as a hobby for R/C car racing over many years. The following link can tell you a little more detail and tell you about the newer LiPO cells:
Model Flight Link