Understanding Battery Life – Part 1

Mobile Computing users (people that use laptops, PDAs, and Smartphones) have one thing in common and that is they all use batteries to power their device. When considering a battery purchase most mobile computing users seek to find the answer to one of the following questions if not all (questions of which relate to the battery); the questions are: What does the life of the battery mean? How is battery life measured? What factors determine battery life? When does the battery begin to lose life? What factors shorten battery life? Is it better to buy a long life battery?

In part 1 of this article series I will look at the meaning of battery life; how battery life is measured; what factors determine battery life and finally when do batteries begin to lose life.

What does the life of the battery mean?

Battery life is the term that is often used when we speak about how long a battery can last (other terms we often use when speaking about battery life is battery capacity, battery runtime, battery mAh, battery milliamp rating, and battery playtime). All these terms speak about the life of the battery – how long the battery will power my PDA (or other mobile computing device) before I have to recharge.

How is battery life measured?

Battery life or is a measurement of capacity. What is Battery Capacity? Battery capacity is a reference to the total amount of energy stored within a battery. Battery capacity is rated in Ampere-hours (AH), which is the product of:

AH= Current X Hours to Total Discharge

What factors determine battery life?

The duration of the battery charge is governed by five factors including:

Physical Size – the amount of capacity that can be stored in the casing of any battery depends on the volume and plate area of the actual battery. The more volume and plate area the more capacity you can actually store in a battery.

Temperature – capacity, or energy stored, decreases as a battery gets colder. High temperatures also have an effect on all other aspects of your battery.

Cut off Voltage – To prevent damage to the battery and the device batteries have an internal mechanism that stops voltage called the cut-off voltage, which is typically limited to 1.67V or 10V for a 12 Volt battery. Letting a battery self-discharge to zero destroys the battery.

Discharge rate – The rate of discharge, the rate at which a battery goes from a full charge to the cut off voltage measured in amperes. As the rate goes up, the capacity goes down.

Battery History – Deep discharging, excessive cycling, age, over charging, under charging, all reduce capacity. Note charging your battery 1 time will reduce capacity as much as 15%-20% depending on your battery's chemistry.

When does the battery begin to lose life?

A battery begins to lose life the very moment is used. Let’s clarify a little more so that we are clear with what that technically means! A new battery is NOT: a battery that was charged, connected to a device, been opened from its wrapping or chemically activated in any way. Now be very careful with any assumption you may have where a battery could still be considered new even after it was charged, connected to a device, been opened or chemically activated in any way. Why?

Inside the battery itself is a system designed to produce a chemical reaction. The chemical reaction is designed for a single purpose: to create an electron flow (i.e. electricity) by which the device is powered. The electron flow is measured (or moves at speeds) in amperes, where 1 ampere is the flow of 62,000,000,000,000,000,000 electrons per second! Therefore once the chemical is activated and the flow of electrons takes place, even for a second, then the loss of power and battery degradation begins and there is no stopping it. Once battery degradation begins a battery is considered used and its natural life will deplete in a matter of time.

One note is that a battery only need be connected to a device or have its connectors touched to effectively create a closed circuit for the chemical to potentially activate, at which point of course the battery life will begin to deplete.

In part 2 of the article on Battery life we will look at the factors that shorten the battery life and whether it is better to buy a long life battery or a lesser capacity battery.