There are a few types of Apple laptops that have third party offerings for high capacity batteries than the stock from Apple. However, I don't think that this is the case with the 15 inch Aluminum PowerBook. Calibrate the battery by running it until the computer is forced to sleep by low battery. Plug it in and recharge the battery. You should be able to get 3-3.5 hours in regular E-mail/word processing, and at least 2 hours under even the most intense usage. If you are getting significantly lower life, Apple is likely to send you a replacement battery.