Compaq nc6000 Lithium-ion battery technology: Getting the most from Smart Batt - Page 5

Smart Battery Technology Estimating battery run time is further complicated by the inaccuracy of the system that monitors and reports the battery charge status to the user. Some notebooks estimate the battery charge state based on manufacturer testing of the specific product model with a particular configuration. This method is inaccurate when another battery with a different state-of-charge is inserted, because charge status of each battery is estimated based on its history in the system. To aid users in monitoring and managing Li-Ion batteries, HP Compaq notebooks provide accurate and instantaneous status information using Smart Battery Technology. HP Smart Battery Technology is based on the Smart Battery System (SBS), which was established by major battery manufacturers in 1995 to promote an industry standard for rechargeable battery technology1. The SBS features a Smart Battery that maintains and reports its own status, thus providing users with accurate information, whether they use different batteries in the same notebook or the same battery in different notebooks. Smart Battery calibration 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 giving the user 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 IC enables precise calibration when the battery is discharged to about 5% of its remaining capacity. Consequently, the user can set the battery alarm at 5% of remaining capacity so that the Smart Battery will calibrate its capacity during normal use. The user simply has 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. 1 For more information about the Smart Battery System, go to http://www.sbs-forum.org/. 5