Drain your battery and then recharge it fully to extend the battery's life.
Battery Drain is a free utility for Mac OS X 10.4 which allows users to charge or drain their batteries to a certain amount for long-term storage.
When storing lithium-ion batteries for an extended period of time, Apple recommends storing them with a 50% charge. Battery Drain allows you to set the charge amount and will automatically shut down the computer when the battery has reached the proper charge.
Battery Drain is useful for administrators of large numbers of portable Macintosh computers, such as iBooks and MacBooks.