Does your Mac portable shut down with 10% battery remaining? Are your time remaining estimates always off? If so, you should calibrate your Mac’s battery. I followed the instructions below and found that my predictive readings were once again accurate.

From Apple.com:

PowerBook G4 (15-inch Double-Layer SD), MacBook (all), MacBook Pro (all)
All other models

1. Plug in the power adapter and fully charge your PowerBook’s battery until the light ring or LED on the power adapter plug changes to green and the onscreen meter in the menu bar indicates that the battery is fully charged.
2. Allow the battery to rest in the fully charged state for at least two hours. You may use your computer during this time as long as the adapter is plugged in.
3. Disconnect the power adapter with the computer still on and start running the computer off battery power. You may use your computer during this time. When your battery gets low, you will see the low battery warning dialog on the screen.
4. Continue to keep your computer on until it goes to sleep. Save all your work and close all applications when the battery gets very low, before the computer goes to sleep.
5. Turn off the computer or allow it to sleep for five hours or more.
6. Connect the power adapter and leave it connected until the battery is fully charged again.