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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