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i/PowerBook battery calibration

PowerBook G4 and iBook: How to Calibrate a New Battery for Best Performance

The battery of an iBook or PowerBook G4 computer has an internal microprocessor that provides an estimate of the amount of energy in the battery during charging and discharging. The battery needs to be recalibrated from time to time to keep the onscreen battery time and percent display accurate. You should perform this procedure when you first use your computer and then every couple of months thereafter.