Battery Education

Understanding Battery Life – Part 3

In my previous two installments of Understanding Battery Life we reviewed what battery life means; how battery life is measured; what factors determine and impact battery life; when do batteries begin to lose life; and how the internal battery design limits the overall capability of the battery. In part 3 of Understanding Battery Life I want to look at two aspects of battery usage that reduces battery life and they are: individual usage patterns and internal technical factors.

Individual Usage Patterns

Using your battery, even only once, will initiate battery degradation. Battery degradation the eventual loss of battery life begins when a user activates their battery (even only once). Furthermore once battery degradation begins there is no stopping it! Activating a battery can be done by charging a battery, connecting a battery to a device, opening a battery or any other actions that would chemically activate the battery! The reason why is because connecting a device for example to a battery creates a closed pathway through which current and the electrons flow through the device to the positive electrode. At the same time, an electrochemical reaction takes place inside the batteries to replenish the electrons. The effect is an electrochemical process that creates electrical energy.

Beyond that first cause in battery degradation there is very little a person can do to speed up the degradation except for the following: use the battery. That is a long-winded way of saying that if you use you will lose it!

I do not mean to say never use your battery – that is not the point – in fact how silly would it be to buy a battery and never use it! The fact of the matter is is that if you were to buy a battery and store it for say 5 years there is a good chance that it would not perform to spec for you because of its age.

If you buy a battery to use in your PDA or other mobile device then of course use it but be aware that by using your battery you are consuming its natural life. The battery was made to be used, to be consumed, and to power your device. So, what we as battery users complain about (short battery life) is not a necessarily a bad battery or a problematic battery (not including potential battery defects) but simply the designed life cycle of the battery.

Before we move to the internal technical factors that affect battery life it is well to point out that using your battery as the primary source for powering your device’s accessories will deplete your batteries capacity faster.

Internal Technical Factors

As pointed out above a battery over time degrades and eventually stops working, this is no surprise, but why this occurs is really a fascinating yet technical process. The reasons are complex issues that are way beyond user control and are wholly contained within your battery and within your device! As we will see these issues (declining capacity, increasing internal resistance, elevated self-discharge, and premature voltage cut-off on discharge) do more to cause Battery Degradation and Power Loss than your typical portable device owner could ever do.

Declining Capacity

Declining capacity is when the amount of charge a battery can hold gradually decreases due to usage, aging, and with some chemistry’s a lack of maintenance. PDA batteries, for example, are specified to deliver about 100 percent capacity when new but after usage and aging a pda battery's capacity will drop. This is normal. If you are using a pda battery (or any lithium-ion or lithium-polymer battery) when your battery's capacity reaches 60% to 70% the pda battery will need to be replaced. Standard industry practice will warranty a battery above 80%. Below 80% typically means you have used the practical life of a battery. Thus the threshold by which a battery can be returned under warranty is typically 80%.

Loss of Charge Acceptance

The loss of charge acceptance of the Li‑ion/polymer batteries is due to cell oxidation. Cell oxidation is when the cells of the battery lose their electrons. This is a normal process of the battery charge creation process. In fact every time you use your battery a loss of charge acceptance occurs (the charge loss allows your battery to power your device by delivering electrical current to your device). Capacity loss is permanent. Li‑ion/polymer batteries cannot be restored with cycling or any other external means. The capacity loss is permanent because the metals used in the cells run for a specific time only and are being consumed during their service life.

Internal Resistance

Internal resistance, known as impedance, determines the performance and runtime of a battery. It is a measure of opposition to a sinusoidal electric current. A high internal resistance curtails the flow of energy from the battery to a device. The aging of the battery cells contributes, primarily, to the increase in resistance, not usage. The internal resistance of the Li‑ion batteries cannot be improved with cycling (recharging). Cell oxidation, which causes high resistance, is non-reversible and is the ultimate cause of battery failure (energy may still be present in the battery, but it can no longer be delivered due to poor conductivity).

Elevated Self-Discharge

All batteries have an inherent self-discharge. The self-discharge on nickel-based batteries is 10 to 15 percent of its capacity in the first 24 hours after charge, followed by 10 to 15 percent every month thereafter. Li‑ion battery's self-discharges about five percent in the first 24 hours and one to two percent thereafter in the following months of use. At higher temperatures, the self-discharge on all battery chemistries increases. The self-discharge of a battery increases with age and usage. Once a battery exhibits high self-discharge, little can be done to reverse the effect.

Premature Voltage Cut-Off

Some devices like PDAs do not fully utilize the low-end voltage spectrum of a battery. The PDA device itself, for example cuts off before the designated end-of-discharge voltage is reached and battery power remains unused. For example, a PDA that is powered with a single-cell Li‑ion battery and is designed to cut-off at 3.7V may actually cut-off at 3.3V. Obviously the full potential of the battery and the device is lost (not fully utilized). Why? It could be something with elevated internal resistance and or PDA operations at warm ambient temperatures. PDAs that load the battery with current bursts are more receptive to premature voltage cut-off than analog equipment. High cut-off voltage is mostly equipment related, not battery.

Concluding Remarks

Now to conclude this 3 part series of Understanding Battery Life lets recap. In part 1 of the series we looked at look at what battery life means; how battery life is measured; what factors determine battery life; and finally when do batteries begin to lose life. In part 2 we looked at the internal design of batteries as their designed potential. Finally in this article we looked at how individual usage patterns and internal technical factors ultimately cause batteries to fail.

Until next time - Dan Hagopian, www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.

Understanding Battery Life – Part 2

In my previous installment of Understanding Battery Life we reviewed what battery life means; how battery life is measured; what factors determine and impact battery life; and finally when do batteries begin to lose life. In part 2 of Understanding Battery Life we will look at a battery’s internal design. A battery design is an important foundation on understanding battery life because of the fact that a battery is a consumable product (a batteries internal chemical is consumed upon activation) and that this consumption shortens the batteries life over time. Therefore to know what the maximum potential of a battery is (the starting point) before the battery is ever consumed is good because once a battery is used even once a battery begins a gradual degradation to the point of no longer being able to power a device (typically about 80% of the batteries capacity – less than 80% capacity is often times too low for a device to recognize the battery).

Initial Technical Ratings

The initial technical ratings of a battery are the specs (the technology) that define the battery. They are represented in most battery websites as the voltage, mAh (battery amperage/capacity), and battery chemistry.  There is much that can be written, and has been written, about each of these factors individually; however, what is key to know about the battery’s technical specs is that they were all decided upon prior to the production of the battery and predestined to operate at specific power levels. Knowing this allows the buyer and seller of a battery to understand in advance how the battery will perform, thus disclosing upfront the capability of the battery.

A battery’s design is a compilation of several required parameters.

• Battery Voltage
• Battery Current
• Battery Capacity
• Battery Chemistry
• Battery Temperature
• Battery Protection Circuitry
• Battery Smart Technology

Before we begin I want to note that Battery Protection Circuitry and Battery Smart Technology require minimal battery usage and although critical components of battery design it is not germane to battery life in great quantity and therefore will not be discussed in this article. I do have more info available on my blog which can be accessed from the links at the end of this article.

Battery Voltage

Critical to battery design is to know how much voltage is required? Voltage is the electrical measure of energy. To know the voltage requirements we need to know the upper and lower voltage range (nominal range).

Battery Current

The second critical key component to battery design is the battery’s current requirements. PDAs, MP3s and other portable devices, for the most part, utilize a constant power discharge to operate. This means that the amount of current will increase as the battery discharges electricity in order to maintain constant power. So we will need to ultimately know the maximum current required. This is important since knowing the max current requirement will influence the necessary protection of chemistry, circuitry, wire, and capacity amongst others. Again we must know the current requirement over the entire nominal voltage range of the battery including start-up currents, surges (intermittent transient pulses). One other important aspect to know about current requirements is the inert current drain of the device. Devices, even when powered down, require small amounts of current to power memory, switches and component leakage.

Battery Capacity

The third key component to know of internal battery design is the necessary battery capacity and runtime. This will define the overall physical size of the battery. Capacity and runtime is measured in Amperes.

Battery Chemistry

When we consider the design capacity we must determine the chemical needed to insure that the necessary runtime will be met. Lithium is used because of its electrochemical properties. Lithium is part of the alkali family of metals a group of highly reactive metals. Lithium reacts steadily with water. In addition the per unit volume of lithium packs the greatest energy density and weight available for this grouping of reactive metals.

Battery Temperature

Ambient operational temperatures are also important because the internal heat of the battery compartment will dramatically affect the life of a battery. Usage and storage patterns are external effect that will also affect battery life and are the responsibility of a user (for example do not leave your device in a hot car with the windows rolled up, or take your device into a sauna).

In my next segment on Understanding Battery Life we will look at two other aspects of battery life and that is how individual usage and internal technical factors affect battery life.

Until next time - Dan Hagopian, www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.

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.

Until next time, Dan Hagopian - www.batteryship.com
Copyright © BatteryEducation.com. All rights reserved.