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HP Notebook PCs - Understanding Lithium-Ion and Smart Battery Technology
One of the most common questions asked by notebook computer users is "How long will the battery last?" The answer is not simple. Users inevitably discover that battery run time varies depending on how and where the notebook is used; however, most users don't understand why the battery sometimes does not last as long as predicted by the battery fuel gauge (Power Meter).
NOTE: Battery life will vary depending on the product configuration, product model, applications loaded on the product, power management setting of the product, and the product features used by the customer. As with all batteries, the maximum capacity of this battery will decrease with time and usage.
As mobile computing becomes more prevalent, users need to understand how environmental and usage factors impact battery run time and life span. This document explains these factors, describes the Smart Battery Technology built into HP notebooks, and recommends practices to maximize battery life.
HP takes safety very seriously and makes battery Material Safety Data Sheets (MSDS) (in English) available that provide general safety information about the third party (non-HP) batteries used in HP products and throughout the industry. In addition, HP works closely with third-party battery suppliers to drive continuous safety and design improvements that help deliver higher levels of safety and reliability. In the unlikely event of a potential safety issue, HP uses proven best-in-class processes and works closely with the appropriate worldwide regulatory agencies to help deliver the highest possible level of safety and best customer experience.
What is a Lithium-Ion battery?
A lithium-ion (Li-Ion) battery pack is made of multiple cells connected in series and in parallel based on the voltage and current requirements of the device. HP notebooks use 3 different types of Li-Ion battery cells: cylindrical, prismatic, and polymer.
Li-Ion batteries are lighter, store more energy, and retain their charge longer than nickel-based batteries of comparable size. Also, Li-Ion batteries can be charged before they are fully discharged because they are not susceptible to the memory effect.
A typical 6-cell Li-Ion battery pack takes 2.5 to 3 hours to fully charge to its maximum voltage with the system in off mode. After the battery is fully charged, current flow to the battery is stopped by a built-in protective (charge control) circuit. The protective circuit prevents the battery from being charged or discharged beyond safe limits.
Although the protective circuit uses a small amount of energy from the battery to operate, the Li-Ion battery self-discharge rate is a fraction of that of nickel-based rechargeable batteries. Some conditions that increase the self-discharge rate of Li-Ion batteries, and should be avoided, are described in the What is Battery Capacity section of this document.
What is Battery Cycle Life?
Battery cycle life is the total number of discharge-charge cycles (Figure 1) a battery yields before it can no longer hold a useful amount of charge. Estimating the cycle life of a rechargeable Li-Ion battery is difficult because cycle life is affected by the average operating temperature of the battery and its energy discharge rate.
Basically, higher temperatures and higher energy discharge rates decrease battery cycle life. The operating temperature of the battery depends on the air temperature as well as the heat generated by the notebook itself and by its immediate environment, such as a docking station. The energy discharge (drainage) rate depends on the type of applications running on the notebook and by its power management settings.
For example, running computer-intensive applications such as CAD, gaming, and DVD movies drains the battery faster and decreases its cycle life more than running word processing applications.
Figure 1: Discharge Cycle
A cycle for a rechargeable lithium-ion battery is the cumulative amount of discharge approximately equal to its full charge capacity. For example, 10 occurrences of a 10% depth of discharge or 2 occurrences of a 50% depth of discharge represent one cycle.
What is Battery Capacity?
Battery capacity is expressed in ampere-hours (Ah). Battery energy, expressed in watt-hours (Wh), is the product of the battery capacity (Ah) and the battery voltage (V). The operating voltage range of a Li-Ion battery pack remains relatively constant throughout its useful life; however, its capacity begins to decrease in a roughly linear manner as soon as it is put into service. New batteries are classified by their rated capacity.
Over time, the actual battery capacity decreases due to electrochemical inefficiencies within each cell. This loss in capacity (aging) is irreversible; it cannot be restored by cycling the battery. Gradually, less and less active material is available within each cell to electrochemically store a charge. Consequently, the user experiences reduced computer run time.
A practical way to express the actual capacity of a battery over time is called full charge capacity (FCC). FCC is expressed as a percentage of the initial rated capacity of the battery. FCC is influenced by the typical discharge load on the battery and by the user profile. Under normal discharge loads, Li-Ion batteries have a life span of between 300 and 500 cycles. With moderate use, Li-Ion batteries are expected to deliver approximately 80% of their rated capacity after 300 cycles or about one year of use (Figure 2). This estimate covers typical users who completely cycle the battery each working day by running low to medium power applications (word processing, e-mail, and spreadsheets) in wired or wireless modes.
Figure 2: Moderate Usage of Fully Charged Battery
Full charge capacity with moderate use is about 80% after 300 cycles.
How does HP determine the Warranty Period?
HP provides a 12-month warranty for Li-Ion batteries. The warranty period is based upon the expectation that the battery will deliver 80% of its initial capacity after 300 cycles at low to moderate power loads. High power loads may cause a battery to reach 80% of initial capacity in less than the 12-month warranty period. Li-Ion batteries will continue to operate below the 80% capacity threshold; however, the capacity (run time) delivered between charges will continue to decrease.
The following table summarizes FCC projections after one year based on 2 user profiles and various power loads. The first profile is for a mobile user who fully discharges and charges the battery almost every working day (300 cycles per year) in a normal environment. The second profile is for a stationary user who only cycles the battery once per week in a high-temperature environment, such as in a docking station. As shown in the table, the additional heat generated by running high power applications or by using a docking station accelerates the loss of capacity.
High power applications may also reduce the battery cycle life by as much as 25%.
What is 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 technology. 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.
For more information about the Smart Battery System, go to http://www.sbs-forum.org/ (in English).
What is 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 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.
Maximizing the capacity and life span of the battery
After reading the information presented in this document, you should be aware that following conditions negatively impact battery run time and life span.
Factors that contribute to loss of battery capacity
Recommended battery care practices
Recommendations for battery use and storage are covered in the HP User Guides for each model. Additional battery care practices are as follows:
Should I fully charge the battery before I use the computer?
No. Lithium ion batteries are more efficient than nickel based rechargeable batteries and go through a formation process during manufacturing. They do not require the initial loading prior to use.
Tips for conserving battery power
You can manually change the power consumption of your notebook PC and conserve battery power.