Giving new life to old laptop and other rechargeable batteries:
Now this isn't for AA, 9V, AAA batteries, etc.; as those have now become so cheap that it would be pointless to try to restore them. The purpose of this technique is for laptop batteries and other proprietary batteries which may be expensive to replace, but have lost their ability to recharge due to sitting around.
There seems to be a caveat that laptop batteries, and other types of rechargeables, become bad just from sitting around and doing nothing; this is not entirely true.
Automated battery chargers, such as though found in laptops, work on a simple principle to recharge a battery; in order for it to recognize and charge the battery, there must be some charge present in the battery. If a battey has been sitting around for some time until it has completely lost its charge, then the charger will not recognize the battery, and the presumption will be that the battery is no good; some batteries, however, can be rescued and used again using this procedure.
The key to restoring a battery is to get the charger to recognize the battery, which means putting a chrage in the battery itself. To do this, one can use a 9V battery, or a 12V lantern battery for newer, higher capacity batteries.
Take the leads from the battery (using wires with a 12V or a snap on cap for the 9V which can be purchased at Radio Shack) and attach (which most likely means to physically hold it) each lead to its corresponding contact on the battery; positive to positive, negative to negative (for some laptop batteries which don't have the contacts marked, you will need to look up a schematic on the web for the battery). Keep the leads held to the battery for anywhere from one minute to several minutes (the larger the capacity battery, the longer you should hold the leads to the battery.
When you are finished, place the battery in the charger or laptop. It may take a while to get the charger to recognize the battery, but be patient. If it recognizes the battery, it will eventually begin to charge it.
Most batteries which have been left sitting for a while will gain a memory; even though they say they are not suppose too. You will likely only get half the life from the battery after doing this, if it works.
Just thought I would share.