Repeated short discharges and recharges cause increasing inaccuracy between the state-of-charge of the battery and the Power Meter readings. Periodically, the battery needs to be calibrated to "relearn" its usable capacity so it can synchronize its charge status with the Power Meter. The calibration procedure maximizes the notebook run time by providing an accurate estimate of the remaining battery charge. Calibration also prevents data loss that can occur during the Hibernation process if sufficient power is not available to complete critical save-to-disk operations.
Smart Batteries calibrate their FCC each time they undergo a full discharge-charge cycle, whether they are recharged in the notebook or in a stand-alone charger/conditioner. Calibration using the notebook is less convenient because it can take up to 4 hours; however, it can lead to more relevant results than using a stand-alone charger.
Calibration results using the notebook are more relevant because the battery relearns its FCC while undergoing a realistic power load. In a stand-alone charger, the battery is discharged using a fixed load. If the fixed load is less than the load typically experienced by the notebook, the learned capacity of the battery may be higher than its actual capacity. In other words, the newly calibrated battery may not deliver the run time predicted by the Power Meter if it is subjected to a greater load than the load used to calibrate the battery.
The accuracy of today’s Smart Battery enables precise calibration when the battery is discharged to about 5% of its remaining capacity. Consequently, you can set the battery alarm at 5% of remaining capacity so that the Smart Battery will calibrate its capacity during normal use.
You simply have to periodically discharge the battery until the 5% capacity alarm is received. The need to perform this procedure will vary with individual use. In general, a Li-Ion battery should be calibrated a minimum of once every 3 months. A battery that is seldom discharged completely should be calibrated about once a month.