Compaq Lithium-ion battery User Manual

Lithium-ion battery technology:
Getting the most from Smart Batteries

Abstract.............................................................................................................................................. 2

Introduction......................................................................................................................................... 2

Lithium-ion batteries.............................................................................................................................. 2

Battery cycle life............................................................................................................................... 3

Battery capacity............................................................................................................................... 3

Warranty period.............................................................................................................................. 4

Smart Battery Technology ..................................................................................................................... 5

Smart Battery calibration................................................................................................................... 5

Battery care practices........................................................................................................................... 6

For more information............................................................................................................................ 7

Abstract

This paper tells HP notebook users how to get the most out of their lithium-ion rechargeable batteries
in terms of run time and lifespan. Detailed in this document are important facts about Li-Ion batteries,
information about HP Smart Battery Technology, and proper battery care practices.

Introduction

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). The
temperature of the battery, the applications running on the notebook, any attached devices, the
brightness of the display, and the notebook power management settings all determine the run time
and lifespan of the battery.

As mobile computing becomes more prevalent, users need to understand how environmental and
usage factors impact battery run time and lifespan. This paper explains these factors, describes
the Smart Battery Technology built into HP notebooks, and recommends practices to maximize
battery life.

Lithium-ion batteries

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. The cylindrical cells are approximately 18 mm
(0.7 in) in diameter by 65 mm (2.6 in) in length, and they are commonly referred to as 18650 cells.
These cells are frequently used in battery packs that are about 20 mm (0.8 in) thick. Prismatic cells
have a slim, rectangular form factor; the most common types are 6-cell and 8-cell Li-Ion battery packs
that are about 12 mm (0.5 in) thick, such as HP MultiBay and tablet PC batteries. Polymer cells are
thinner than prismatic cells. They are often used in products such as the IPAQ Pocket PC and some
ultra-portable PCs, which require battery packs less than 10 mm (0.4 in) thick.

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 "Battery capacity" section.

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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 compute-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. 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.

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 lifespan 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. Full charge capacity with moderate use is about 80% after 300 cycles.

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