1. Put the dead laptop battery in a sealed plastic bag.
2. Put the bagged battery in the freezer for about 12 hours.
3. Take the bag out of the freezer, and let the battery warm up to room temperature, drying it occasionally with a towel if it appears damp.
4. Put the battery back into your laptop.
5. Charge the battery as much as possible, then leave the laptop on in order discharge it completely. Repeat this step 3-4 times.
6. Your formerly-dead battery should now be much more usable, if not totally restored.