Reviving a dead laptop battery

Li- Ion chemistry batteries can occasionally be brought back to life, however it is not without some risk. Li-Ion or Li-Poly chemistry has threshold voltages that the batteries must be kept within, you can do some research on this battery chemistry for model aircraft use and get more and better info than space will allow here. You will need to 'cycle' your battery to bring the capacity back to almost normal. You will need to discharge the battery out of the laptop via jumper connectors, and recharge while MONITORING the battery a number of times. You can discharge through the laptop, but you wont be able to monitor the voltage or control the rate of discharge (risky). Finding a hobbyist with the proper chargers to charge and discharge Li-xx chemistry batteries is the safest way to go, as you will charge outside the laptop and be safer in the event of fire. Do not under any circumstance dismantle the battery housing, you risk causing a fire due to puncturing the membrane and shorting the cells internally. The batteries are great, the technology buried in your laptops' charge circuitry does a fine job of masking the inherent danger of fire.

This depends on the battery type, lead-acid (Pb-Acid) and nickel-cadmium (NiCd) can sometimes benefit from a low-current trickle charge after a full discharge; this can take a full day or longer.

Lithium-Ion (Li-ion), which is likely what you have, and Nickel-Metal-Hydride (NiMH) do not benefit much from attempting this, although they can benefit at times from charging from a near empty state to full, usually in a cool environment, though freezing is not something I've heard of as being successful.

When your battery is dead, it's usually just one cell of the battery that is dead. Some batteries are constructed in a manner that clearly shows AA, C or D cells soldered together and shrink-wrapped. In this case, you can often buy a bunch of batteries of this type and the same chemistry and replace them for less than buying the custom pack. Most laptops today have a Lithium-Ion polymer battery which is a custom shaped blob of chemical you don't want to mess with, but you can sometimes find after market replacements for less than what the original manufacturer would sell them to you for, IE newertech.com makes nupower batteries for older iPods, panasonic can sometimes be found selling a battery that fits your specs if you're willing to reuse the old casing and control circuits.

Generally speaking, you should buy a new battery from the equipment manufacturer.