If you are a Mac user, and you have an iBook, Powerbook, Macbook, or Macbook Pro, then you need to calibrate your battery every couple of months.
Here’s how:
How to calibrate the battery on your iBook, Powerbook, Macbook, or Macbook Pro
NOTE: The iBook and Powerbook has different instructions than the Macbook and Macbook Pro, as you’ll see on the above article.