Overview

Power sources refer to all types of technology that can provide power to a system including AC outlets, fuel cells, photovoltaic cells, and batteries. Batteries are the most common type of power source for portable electronic devices although fuel cells are showing great promise for the future.

Many portable electronic devices are capable of utilizing power from an AC power outlet, but almost all use some type of portable power storage technology. If AC power is used, it is generally for the purpose of extended use or for recharging the system battery.

Battery technology has been evolving very rapidly in recent years to meet the demands of the portable electronics industry. Advances in battery technology have contributed greatly to the extreme miniaturization that has taken place.

There are many types of batteries that use a wide variety of wet and dry chemistries. We will only discuss batteries that are of interest for portable electronic applications.

Batteries are usually divided into two types: primary and secondary. Primary cells are intended to be charged once, used until discharged, and then discarded. Secondary cells have the ability to be recharged and discharged many times.

Energy density is a measure of how much energy a battery can store in a given volume or mass. Volumetric energy density is usually measured in watthours per liter (Wh/L). Gravimetric energy density is generally measured in watthours per kilogram (Wh/kg).

Some secondary batteries exhibit a behavior known as memory effect. When these batteries...