BatteryEducation – Page 32 – Battery Education

How Many Cells Are In A Battery

Question from a reader: “How many cells are in the Toshiba Satellite M105-S3041 Laptop Battery? The battery is for a Toshiba Satellite M105-S3041 and its technical ratings are 10.8 volts 8800 mAh, Lithium Ion

The question from the reader is a great question for it gets to the heart of battery manufacturing and begins to unravel the power of a battery. The answer is simply: 12 cells. But what does the answer mean and how does the number of cells relate to the overall value of a battery? Let’s find out…

What is a Battery and How Does it Create Energy?

A battery is a device that converts chemical energy into electrical energy. Batteries have two electrodes, an anode (the negative end) and a cathode (the positive end). Collectively the anode and the cathode are called the electrodes. What is positve and what is the negative terminal? It would be great to simply say that the anode is negative and the cathode is positive, however, that is not always the case. Somtimes the opposite is true depending on battery technology.

In between the battery’s two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. The voltage runs through a chemical called an electrolyte (which can be either liquid or solid). This battery consisting of two electrodes is called a voltaic cell.

Therefore batteries in effect create electrochemical energy. In order to convert chemical energy into electrical energy there is a chain of events that have to occur prior to the creation of electrical energy. Key to the creation of electrochemical energy in batteries is that electrical energy is injected into two chemicals in a solution. Electricity is introduced into a battery via a charger. The charger acts as a conduit of the pushing electrons that are forcing their way into the chemical lithium. This charge process involves intercalation: the joining of a molecule (or molecule group) between two other molecules (or groups). Intercalation is the process of ions being pushed by electrical current into solid lithium compounds. Lithium is one of the chemical components used to create electrical energy in batteries. Lithium compounds have minuscule spaces between the crystallized planes for small ions to insert themselves from a force of current. Ionizing lithium loads the crystal planes to the point where they are forced into a current flow. Intercalation replenishes, in effect, lithium but the net result of ionization is the ultimate depletion of the lithium reactive property. You could say if you use it you will lose it!

But what makes lithium good for batteries is that lithium is one of the metals in the alkali group (the other metals include Sodium, Potassium, Rubidium, Cesium, and Francium). Lithium is a highly reactive metal. Lithium has only one electron in its outer shell (two electrons in its inner shell), which makes it chemically “ready” to lose that one electron in ionic bonding with other elements. Lithium is used as a battery anode material (due to its high electrochemical potential). Electrochemical potential is the sum of the chemical potential and the electrical potential. The higher the electrochemical potential the better the electrical current yields. In some lithium-based cells the electrochemical potential can be five times greater than an equivalent-sized lead-acid cell and three times greater than alkaline batteries. One other core advantage that lithium has is that it is soft and bendable which allows for tight configurations in small cell designs (PDAs. Laptops, Cameras etc…).

What Type of Lithium Cell is Used in Laptops

Now this brings us to battery cells and our original question from the reader. Lithium based battery cells are good but there are a variety of lithium based battery cells. For example the lithium based cell identified as 18650 is one of the most common battery cell on the market for laptops. 18650 is manufactured by many manufacturers including many private branded companies to public companies like LG, Sony, Sanyo, Samsung, Panasonic.

18650 is a 3.6V cylindrical Li-Ion cell. 18650 has no memory effect (distinguish between digital memory effect) and longer storage life than NiMH battery cells. 18650 is light weight and has a high energy density. It is in effect perfect for building batteries for laptop and other portable power devices.

The additional technical specifications for the 18650 battery cell include:

Nominal Voltage Average 3.7 V – the concept of nominal voltage is that voltage range exists depending on the number of cells in the battery.
Nominal Capacity – 2200 mAh (above 2200 the stability of lithium based cells is called into question)
• Max. Charging Current – 2.4 Amps Max.
• Max. Discharging Current – 4.6 Amps max.
• Dimensions (DxH) 18.3 mm (Max 18.4) x 64.9 mm (Max 65.1)
• Weight 46.5 g (1.64 oz)
Internal Impedance Internal Impedance: less or equal to 90 ohms
Cycle Performance is 80% of initial capacity at 300 cycles

Now as stated above the reader asked how many cells were in the Toshiba Satellite M105-S3041 Laptop Battery? The battery is rated at 10.8 volts and a capacity of 8800 mAh.

As I mentioned above the nominal voltage average is 3.7V. Some manufacturers may use 3.6V and some may use 3.7V. In the case of a laptop battery with 10.8V the nominal voltage rating used is 3.6V. Thus if we divide 10.8V by 3.6V we get 3. Thus 3 cells in a series. We also know that the batteries capacity is 8800 mAh. We know the nominal capacity is 2200 mAh. Therefore if we divide 8800 mAh by 2200 mAh then we get 4 in parallel.

Therefore we have 3 cells in series X 4 cells in parallel equals 12 cells in total.

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

Voltage Failure Modes

Question from a reader: "Hi Dan, What is the failure mode for Lithium Polymer batteries? I understand that Nickel Cadmium batteries fail as a short circuit usually. Therefore, a pack of NiCads will continue to operate with a shorted cell but with a voltage that is one cell lower. Do LiPo's fail…resulting in the loss of the entire pack? Thanks

Answer:

First of all the reference to a "failure mode" is not necessarily a singular event. It is in effect a catch-all phrase representing potential problems. I wrote an article series on the concept of Battery Failure Mode and Effects Analysis. But this concept is not new but is manufacturing quality assurance analysis, in essence, be applied to every industry.

The article series can be accessed at:

Part 1
http://www.batteryeducation.com/2008/07/battery-failure.html
Part 2
http://www.batteryeducation.com/2008/07/battery-failu-1.html
Part 3
http://www.batteryeducation.com/2008/07/battery-failu-2.html

Specific to your question on lithium polymer batteries there could be a number of "failure mode(s)" and sub-failure modes related to the manufacturing and personal usage of a battery including Li-Po chemistry based cells. For example:

Batteries can have faulty cell design
Batteries can be manufactured under uncontrolled processes
Batteries can be operated in uncontrolled conditions
Batteries can be abused
Batteries can degrade and lose power

For more information on these examples please see:
http://www.batteryeducation.com/2006/06/what_causes_bat.html

Heat and water for example are not good for any battery. But it is surprising to me how many people use their battery and device in both and of course that represents several failure modes. An example is when one of our customers several years ago always took his iPod mini into the sauna at his gym. Well that is not the best place for a battery or device. Eventually his battery died and so did the device. That is a bad failure mode brought about be a user. Another example is when there are metallic electrode shavings evident in the batteries electrolyte. When current is running from one electrode to another through the electrolyte the shavings cause any battery to short circuit. The short circuiting could result in the battery smoking, bubbling or stopping. That is an example of bad manufacturing and of course a failure effect. Another example of a failure mode is when you open the battery casing. If you open the casing once it is sealed hermeneutically then you run the big risk of causing a failure mode to occur.

In any event – any failure mode will cause a battery to either operate at a lower performance than originally designed or stop working period. One interesting side note is that devices can operate with a battery that is at a lower voltage (but not higher voltage) as the device originally manufactured. The reason is because a battery's voltage is not necessarily a static measurement.

Volts – or V – are an electrical measure of energy potential. Voltage can also be thought of as the amount of "pressure" of electrons that pass from a negative connector to a positive connector. Or V can be defined as the measure of the strength of an electrical source of power for a given current level.

Voltage can also be defined as the Electrical Potential difference – a quantity in physics related to the amount of energy that would be required to move an object from one place to another against various types of force. In the fields of electronics the electrical potential difference is the amount of work per charge needed to move electric charge from the second point to the first, or equivalently, the amount of work that unit charge flowing from the first point to the second can perform.

Mathematically voltage is commonly measured by V= I x R; where V=Voltage, I=Current, R=Resistance.

Beyond the definition what challenges many is the confusion that a battery contains four unique types of voltage measurements.
Each voltage measurement type residing in a battery effects battery life.

Float Voltage – is battery voltage at zero current (with battery disconnected).
Nominal Voltage – is battery voltage range 3.7V, 5.2V, 10.2V, 12V etc that says that a voltage range exists depending on the number of cells in the battery. For example a 12 Volt battery is made of 6 cells and has a Float voltage of about 12V.
Charge Voltage – The voltage of a battery while charging.
Discharge Voltage – The voltage of a battery while discharging. Again, this voltage is determined by the charge state and the current flowing in the battery.

So in effect it is possible that a device will operate on a battery at lower voltage. I hope this answers your question.

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

Battery Manufacturing and Cell Grades – Part 2

Battery cell grades are a classification system that manufacturers use to distinguish the benefits of capacity and runtime.

What are battery cell grades? How do manufacturers use cell grades in the manufacturing of batteries? How do the different grades affect the quality of a battery? In part 2 of this article series we will continue where we left off and look at the battery cell grade classification system that battery manufacturers use during the process of collecting raw battery material, developing design specifications, and assembling packs for various consumer and industrial applications.

Battery cell grades are a classification system that manufacturers use to distinguish the benefits of capacity and runtime. Before I unpack that answer we need to understand that battery grades are not a measure of quality! Battery grades do not imply that one grade is “better” than another but a reflection of capacity and internal resistance at different price points. Before I continue with cell grades it is important to understand capacity and internal resistance.

Battery capacity quantifies 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. Battery capacity is measured in amperes, which is the volume of electrons passing through the batteries electrolyte per second. A milliAmp hour (mAh) is the most commonly used notation system for consumer electronic batteries. Note that 1000 mAh is the same as 1 Ah. (Just as 1000mm equals 1 meter). In essence more capacity equals longer runtime between battery charges.

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. Internal resistance is caused primarily from the opposition of current by the electrolyte that resides between a battery’s two electrodes.

Now battery cell grading is a process of categorizing cells into grades (Grade A, Grade B, and Grade C). Every grade is important to the manufacturer, meaning there is not one grade that is better than another. In fact every manufacturer wants to make and sell each cell grade because of the unique differences of each grade and because each cell grade has a specific market and device segment.

As mentioned above cells are always categorized to be graded A, B and C but there is not a single manufacturing standard for categorizing cells; each manufacturing factory may have their own standard so thus cell grade categorization is not necessarily scientific.

For example, Li-ion cell 053450, some companies may categorize the cell as follows

Grade A— capacity above 1000mAh, internal resistance below 60mΩ
Grade B—capacity 900 to 1000mAh, internal resistance 60mΩ to 80mΩ
Grade C—capacity below 900mAh, internal resistance above 80mΩ

But for some companies with better production lines and capability, they may have higher capacity cells so they may categorize cell 053450 as follows:

Grade A— capacity above 1100mAh, internal resistance below 60mΩ
Grade B—capacity 1000 to 1100mAh, internal resistance 60mΩ to 80mΩ
Grade C—capacity below 1000mAh, internal resistance above 80mΩ

One generally accepted conclusion can be drawn from these two examples and that is grade A cells have the longest runtime and cycle life, grade B has the second longest runtime and cycle life and grade C has the third longest runtime and cycle life.

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

Battery Manufacturing and Battery Cell Grades – Part 1

What is involved when a battery is manufactured? What materials are needed to manufacture a battery? What are battery cell grades? What do battery grades mean? How do the different grades affect the quality of a battery? How can you know what battery grade you have? And is any one grade more important then another?

To understand battery cell grades we have to understand how batteries are manufactured. Battery manufacturing involves the collection of raw material, the development and setting of design specifications, and the assembly of an individual battery pack. On a very high level that is ultimately what is involved when a battery is made. Furtherore battery manufacturers utilize manufacturing principles, much like manufacturers of other products, to get the batteries made efficiently and effectively.

When it comes to the collection of raw materials manufacturers have to collect very specific material to be used in the assembly of battery packs. This material includes the following:

The casing – for enclosing and hermetically sealing a battery body – is manufactured in one, two, or three layers that include for example polyethylene terephthalate layers, a polymer layer, and a polypropylene layer.

The chemistry which is often times lithium based for its high electrochemical potential. An example could be a {Solution of Lithium hexaflourophosphate (LiPF6) – a mixture of Organic Solvents: [Ethylene Carbonate (EC) + DiEthyl Carbonate (DMC) + DiEthyl Carbonate (DEC) + Ethyl Acetate (EA)]}.

The electrolyte – The actual conversion of chemical energy into electrochemical energy can only be done if an electron flow passes between two electrodes, an anode (the negative end) and a cathode (the positive end). The battery’s electrical current (electron flow) runs from one electrode to another through a conductive chemical called an electrolyte solution.

The battery’s specialized hardware that includes: the connector, the fuse, the charge and discharge FETs, the cell pack, the sense resistor (RSENSE), the primary and secondary protection ICs, the fuel-gauge IC, the thermistor, the pc board, the EEPROM or firmware for the fuel-gauge IC..

Now part of the manufacturing process is the categorization of battery cells. Categorizing battery cells are done in grades (Grade A, Grade B, and Grade C). In part 2 of this article series I will explain what the different grades mean and how manufacturers use the different grades and what the grades mean to you and your battery.

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

Rechargeable Batteries Can Only Be Charged 300-500 Times – Part 2

In the last two articles we addressed how and why rechargeable batteries have limited charge cycles. We reviewed in detail the effect of a charge-discharge cycle – a chemical change in a battery system that results in degradation and power loss. But there is one aspect in my last article that deserves special attention. This one factor is the basis of battery degradation. It is the reason why batteries can never just keep going and going and going. The fact is, is that all batteries degrade and lose power because there is a reduction in the battery’s active material.

We know that a battery is a device that converts chemical energy into electrical energy. In order to convert chemical energy into electrical energy there is a chain of events that have to occur prior to the creation of electrical energy. The chain of events have been discussed in depth in previous articles which you can access on my blog but what is key to the creation of electricity is that in batteries electrical energy is produced from two chemicals in a solution. After discharging you recharge the battery via a charger. The charge process involves intercalation: the joining of a molecule (or molecule group) between two other molecules (or groups). Intercalation is the process of ions being pushed by electrical current into solid lithium compounds. Lithium is one of the chemical components used to create electrical energy in batteries. Lithium compounds have minuscule spaces between the crystallized planes for small ions to insert themselves from a force of current. Ionizing lithium loads the crystal planes to the point where they are forced into a current flow. Intercalation replenishes, in effect, lithium but the net result of ionization is the ultimate depletion of the lithium reactive property. You could say if you use it you will lose it!

Why then is lithium used as the chemical to create electricity in batteries? There are a number of good reasons – let’s look at a few!

General Characteristics of Lithium

Name: lithium
Symbol: Li
Atomic number: 3
Atomic weight: [6.941 (2)] g m r
CAS Registry ID: 7439-93-2
Group number: 1
Group name: Alkali metal
Period number: 2
Block: s-block
Standard state: solid at 298 K
Color: silvery white/grey
Classification: Metallic

Lithium is one of the metals in the alkali group (the other metals include Sodium, Potassium, Rubidium, Cesium, and Francium). Lithium is a highly reactive metal. Lithium has only one electron in its outer shell (two electrons in its inner shell), which makes it chemically “ready” to lose that one electron in ionic bonding with other elements. Lithium is used as a battery anode material (due to its high electrochemical potential). Electrochemical potential is the sum of the chemical potential and the electrical potential. The higher the electrochemical potential the better the electrical current yields. In some lithium-based cells the electrochemical potential can be five times greater than an equivalent-sized lead-acid cell and three times greater than alkaline batteries. One other core advantage that lithium has is that it is soft and bendable which allows for tight configurations in small cell designs (PDAs. Laptops, Cameras etc…).

Lithium, even with all of its good chemical properties will eventually, however, react to the point where the electrochemical potential will yield a charge that is simply not enough to create current to pass to power a device.

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

Rechargeable Batteries Can Only Be Charged 300-500 Times – Part 1

A charge-discharge cycle involves draining or using your battery to where there is for all intensive purposes, no charge left, and then subsequently charging the battery with a power adapter to 100% capacity. This process of charging and discharging (charge cycling) can only be done between 300-500 times. The question that we want to address is why? Why is it that lithium batteries can only be charged less than 500 times? Why does a battery over time degrade and eventually stops working and what if any does the reduction of the battery's active material and subsequent causes of chemical changes effect battery degredation?

In my last article I explained how that the simple task of charging a battery is far from easy. For example I examined how a battery, a device that converts chemical energy into electrical energy, has two internal electrodes – an anode (the negative end) and a cathode (the positive end), and that between the two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. We learned that batteries are made up of plates of reactive chemicals (Li-ion, Li-po, NIMH, NICD) separated by an electrolyte barrier (which can be either be in a liquid, solid, or gel state), and subsequently polarized so all the electrons gather on one side. We looked at how electricity is produced through a chemical change inside the battery system. We also learned that batteries require electricity to produce electricity and that the introduction of electricity involves replenishing the electrons in the lithium chemical and this chemical process is called intercalation, which, is the joining of a molecule between two other molecules. So without question charging a battery is anything but easy.

One other thing we learned that has helped shape this article is that a charge-discharge cycle involves draining or using your battery to where there is for all intensive purposes, no charge left, and then subsequently charging the battery with a power adapter to 100% capacity. This process of charging and discharging (charge cycling) can only be done between 300-500 times. The question that we want to address is why is it that lithium batteries can only be charged less than 500 times?

Battery Degradation and Power Loss

A battery over time degrades and eventually stops working, this is no surprise, but why this occurs is really a fascinating yet technical process. These reasons are complex issues that are way beyond user control and are wholly contained within your battery and within your device! These technical processes are a result of the reduction of the battery’s active material and subsequent causes of chemical changes. The chemical changes that I write of are:

Declining capacity – when the amount of charge a battery can hold gradually decreases due to usage, aging, and with some chemistry, lack of maintenance.

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 discharge 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, 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).

All batteries have an inherent elevated 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 chemistry 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 utilized).

Now that we have looked at how the chemical changes in a battery effect battery degradation and power loss and contribute to the eventual total loss of the battery I will, in my next article, discuss why battery degradation occurs in the first place.

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

How Many Times Can I Charge My Battery?

500 million lithium batteries are in use today. A very big number indeed and the chances that you are one of them are quite high. You could have a laptop, PDA, MP3 or even a cell-phone, all of which more likely than not has a lithium ion or a lithium polymer chemical based battery system. If so then one question that you will have eventually is how many times will I be able to charge the battery before it is effectively dead? Is it 300 times, 400 times, or 500 times? The answer is between 300-500 times.

But what does that answer mean? As this article will explain the charge cycle is quite complex and involves the replenishment of electrons. In order to get a beginning understanding of what actually is taking place during a charge and discharge cycle we need to understand: what a battery is, how it works, what it produces, and finally what happens when you charge and discharge.

What is a Battery?

As I have written in other articles a battery is a device that converts chemical energy into electrical energy. Batteries have two electrodes, an anode (the negative end) and a cathode (the positive end). Collectively the anode and the cathode are called the electrodes. What is positve and what is the negative terminal? It would be great to simply say that the anode is negative and the cathode is positive, however, that is not always the case. Somtimes the opposite is true depending on battery technology. In between the battery’s two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. The voltage runs through a chemical called an electrolyte (which can be either be in a liquid, solid, or gel state). This battery consisting of two electrodes is called a voltaic cell. Most batteries today are advance forms of the voltaic cells and have additional technology packed into the battery casing to support the overall system and its connected device. These controls include the connector, fuse, charge and discharge FETs, the cell pack, the sense resistor (RSENSE), the primary and secondary protection ICs, the fuel-gauge IC thermistor, pc board, and the EEPROM or firmware for the fuel-gauge IC.

How Does a Battery Work and What Does It Produce?

We know that the result of a battery converting chemical energy into electrical energy allows us to turn on our laptop, PDA, MP3 or even a cell-phone. But how does the conversion process take place? As stated above the batteries we use today are variable changes of the voltaic pile. In addition to the controls I listed above today’s batteries are made up of plates of reactive chemicals (Li-ion, Li-po, NIMH, NICD) separated by an electrolyte barrier (which can be either be in a liquid, solid, or gel state), and subsequently polarized so all the electrons gather on one side. The system was designed to separate both positive and negative electrons. Then after separation an electron exchange occurs and a current of electron flow moves electrons to and from the anode and cathode. Simultaneously an electrochemical reaction takes place inside the battery to replenish the electrons. The effect is a chemical process that creates electrochemical energy.

Now the electrochemical reaction that is taking place is a chemical change that is necessary in order to create electricity. One factor that needs to be understood is that electricity is the flow of electrons. Specifically, electricity is a property of subatomic particles which couples to electromagnetic fields and causes attractive and repulsive forces between them. This repulsive force between the subatomic particles creates an electric current; the flow of electric charge transports energy from one atom to another. This electrical current is measured in amperes, where 1 ampere is the flow of 62,000,000,000,000,000,000 electrons per second!

Electricity therefore is a created energy source. All electricity in fact is a created source made or converted from coal, natural gas, oil, nuclear power, wind, heat, sun, water, biomass and or other chemicals. In batteries today electricity is created by two chemicals in a solution for example: {a Solution of Lithium hexaflourophosphate (LiPF6) – a mixture of Organic Solvents: [Ethylene Carbonate (EC) + DiEthyl Carbonate (DMC) + DiEthyl Carbonate (DEC) + Ethyl Acetate (EA)]}

Charging and Discharging Your Battery

Charge cycling a battery means to completely discharge (or drain) a battery’s created electricity to where there is a charge of less than a 1% capacity remaining. At this point the power to the device will cease and your device will power off. Then after the power is off you recharge the battery to 100% capacity using a power adapter either from a wall socket for example. Regardless of how you charge the battery that process of discharging and charging represents one complete charge cycle.

I noted above that an electrochemical reaction takes place inside the battery to replenish the electrons. The effect is a chemical process that creates electrical energy (electrochemical energy). Lithium is used, amongst other chemicals, as a battery anode material due to its high electrochemical potential. In fact the energy of some lithium-based cells can be five times greater than an equivalent-sized lead-acid cell and three times greater than alkaline batteries. Lithium cells often have a starting voltage of 3.0 V. This means that batteries can be lighter in weight, have lower per-use costs, and have higher and more stable voltage profiles.

Charging lithium can be thought of as the introduction of ions or movement of chemistry. To move the lithium chemistry (lithium-ion, lithium polymer, lithium iron phosphate, etc) you have to have a minimum voltage applied to the lithium. Most battery cells are charged to 4.2 volts with relative safe workings at about 3.8 volts. Anything less than 3.3 volts will not be enough to charge or move the chemistry. One thing to note here is that volts are an algorithmic measurement of current. So in a sense to create current through your battery you have to introduce current into your battery’s lithium .

Introducing current into your lithium is called intercalation. Intercalation is the joining of a molecule (or molecule group) between two other molecules (or groups). When it comes to charging your battery you are in effect pushing ions in and out of solid lithium compounds. These compounds have minuscule spaces between the crystallized planes for small ions, such as lithium, to insert themselves from a force of current. In effect ionizing the lithium loads the crystal planes to the point where they are forced into a current flow. The current flow is then channeled back and forth from anode to cathode and thereby creating an electrical flow to power on your device. Again this can done 300-500 times. In my next article we will look at why batteries have limited charge cycles.

Lithium Ion Batteries Are Sensitive to Heat

Over 15 million students are enrolled in fall college classes across the United States according to a US Census Bureau study in 2004. Using that number as a base it can be projected that the fall of 2008 should see a slight up-tick in college enrollees. Interestingly the number of college students that are going to college with laptop computers have increased by 28% compared to 42% of college students in 2004. This means that nearly 70% of enrolled students are using laptop computers. In real numbers that represents 10,500,000 laptop computers.

Now listen up college students – your laptop battery is more than likely a Li-ion battery and if it is then there is a natural tendency to keep your laptop plugged into a wall outlet when you are close to one. You may also find that you are actually “plugged” in to a wall outlet more than you are not and there in lies a problem. When your laptop is plugged into a wall outlet your battery heats up big time and heat and lithium do not mix well together.

Hold on! You have to charge battery. Yes that is true, but you do not have to keep your laptop plugged into a wall outlet for the entire school year! But won’t that reduce my battery life if I’m constantly powered from the battery?

Your battery will diminish in capacity – the ability to charge and power your laptop. That is a fact and a natural consequence of batteries today. This diminishing power performance is called battery degradation and power loss. I have written on this topic before and you can read about it on my blog but on a high level a battery over time degrades and eventually stops working, this is no surprise, and it occurs due to the following technical processes: declining capacity, increasing internal resistance, elevated self-discharge, premature voltage cut-off on discharge.

So should you constantly keep your battery charged at 100% capacity? No you should not. Why? To answer that question let’s look at what is occurring when you charge a battery. When charging your battery you are forcing electrical current into a battery cell from a charger. The force of electrical current causes temperature increases.

Now it is true that contained within your laptop battery are integrated power management circuits that are designed to protect against over-voltage and under-voltage conditions that increase heat in the battery but one factor of how well a battery is being protected during a charge depends on the ratio of the heating rate versus the dissipation rate. If the heating rate is higher then the dissipation rate then thermal runaway will occur (leaking, smoking, gas venting, flames).

Now don’t go into panic mode since the integrated circuits are really good at keeping the heating rate lower than the dissipation rate and you are in extremely minimal danger of thermal runaway occurring. But the practice of keeping your battery charged continuously can negatively affect your battery’s longevity. So charge your battery and then run your laptop on battery power until you have to charge it again.

Digital Memory Effect on Batteries

Have you ever wished that you had an extra 20 minutes of battery life left in your portable device? How about an hour! A real difference exists between the life of your battery and the displayed battery charge meter on your device? How big of a difference? How often does it occur? Why does it occur? What can be done? In this article we will look at these questions and learn about what you can do to reduce power waste and maximize your battery life.

Help my batteries dead and I can’t power on! The cultural expression of a “dead battery” is the habitual practice that occurs in place of the more technically appropriate reason of declining capacity. Declining capacity is when the amount of charge a battery can hold gradually decreases due to usage, aging, and with some chemistry, lack of maintenance. Declining capacity is inherent in the ultimate design of a battery – due to limitations with technology - you could consider it the natural side effect or wear and tear of the battery (other wear and tear aspects includes increasing internal resistance, elevated self-discharge, and premature voltage cut-off on discharge).

But there is a real problem with declining capacity and that is the capacity that is measured by your device and displayed to you on your battery charge meter is not always correct. Your device could be reading a digital imprint instead of the actual hardware that transmits capacity back to the device. The digital imprint (digital memory effect) causes your device to use the incorrect reading as its base measuring capacity. This action results in forcing a premature voltage cut-off on discharge, which is when a device does not fully utilize the low-end voltage spectrum leaving unused power in the battery. Another fancy word for leaving unused power in your battery is “waste”. Let’s find out what can you can do reduce power waste and maximize battery life by looking at:

What is the Digital Memory Effect?
What Can Be Done To Correct the Digital Memory Effect?

What is the Digital Memory Effect?

The digital memory effect is a failure mode (see my article series on Battery Failure Mode and Effects Analysis) whose effect results in the transmission of improper calibrations of the battery’s fuel gauge to a device.

Now let’s unpack that answer to discover its real meaning.

First we must distinguish between memory effect and digital memory effect. A memory effect is the concept that was derived from cyclic memory. Cyclic memory is the thought that a battery could “remember” how much energy was used up on previous discharges. Cyclic memory only affects nickel-cadmium batteries. Since we are strictly focused on lithium ion and lithium polymer chemistries I don’t want to get into the chemical change that occurs at the molecular level (crystal growth and concealment of active electrolyte material) but simply will state that the memory effect is the common term people use when there is a voltage depression problem with a battery. Voltage depression causes the inaccurate measurement and subsequent unnecessary charging of a battery.

Inaccurate measurement of capacity is the only similarity between memory effect and digital memory effect since digital memory effect has nothing to do with molecular chemical change. Instead digital memory effect is the improper calibration and reading by the device and the battery’s fuel gauge.

More specifically, inside a battery (or more correctly stated smart battery) is specialized hardware that provides calculated on demand current as well as predicted information to and from the device and includes:

the connector
the fuse
the charge and discharge FETs
the cell pack
the sense resistor (RSENSE)
the primary and secondary protection ICs
the fuel-gauge IC
the thermistor
the pc board
the EEPROM or firmware for the fuel-gauge IC.

In addition to the above advanced chip components information flows from these components to the device through the System Management Bus (SMBus) control – a two-wire interface through which simple power-related chips can communicate with rest of the system. The SMBus allows a device to transfer manufacturer information, transfers model or part number to and from the device and battery, save its state for a suspend event, report different types of errors, accept control parameters and return its status.

Now with that back drop of information we can address the digital memory effect. As alluded to above the fuel gauge integrated circuitry calculates remaining battery capacity (power) and transmits that calculation to the device operating system through the SMBus connectors. The fuel gauge also stores present cell capacity characteristics and application parameters within the on-chip EEPROM (electrically erasable programmable read only memory). The calculated capacity registers a conservative estimate of the amount of charge that can be removed given the current temperature, discharge rate, stored charge and application parameters. Capacity estimation is then reported in capacity remaining and percentage of full charge to the device.

But sometimes the reported information is not correct. The incorrect report of capacity remaining and percentage is caused by the fuel gauge not recalibrating its circuitry automatically. The digital memory effect is then a false reading for maximum capacity and thus results in lower battery run time.

What Can Be Done To Correct the Digital Memory Effect?

To correct the digital memory effect and properly recalibrate the fuel gauge circuitry simply do a full cycle discharge/recharge every several dozen charges. There is no real hard number. If you have never done a complete discharge then do so now. By performing a complete discharge you will cause a manual reset of the fuel gauge circuitry and will eliminate the digital memory effect.

Battery Safety Guidelines

Have you ever held a battery before? Did you know that a battery though relatively safe can act and operate like a mini bomb? Don’t worry your next battery more than likely will not explode on you if handled correctly. In fact in excess of 100 million battery related devices have been bought by consumer since 2003 (that is a conservative number). So the 339 incidents report by the Consumer Product Safety Commission represent .000003 (a very small percent) of all battery related devices on the market. So the likelihood of your next battery exploding is highly unlikely. However if you ever use a battery or plan on using a battery you should know how to handle and maintain basic battery safety guidelines. In fact as a general rule of thumb battery packs have to be:

Batteries have to be stored safely
Batteries have to be charged correctly
Batteries have to be protected from unexpected damage
Batteries have to be handled safely

Batteries have to be stored safely

Batteries can be stored both indoors and outdoors as long as batteries are kept in cool conditions without direct sun light on the battery or battery storage box or container. Batteries should be stored in a dry location with low humidity, and a temperature range of –20°C to +30°C. Batteries can be stored for a long time however the longer the storage time is the faster the acceleration of the battery’s self-discharge which can lead to the deactivation of the batteries. To minimize the deactivation effect, store battery packs in a temperature range of +10°C to +30°C. Also if a battery has been stored for a long period of time please note that the deactivation of the batteries may have led to decreased capacity. To recover batteries in this state simply repeat several cycles of fully charging and discharging. Also when storing packs for more than 6 months be sure to charge the battery at least once every 6 months to prevent leakage and deterioration in performance due to self-discharging.

Batteries have to be charged correctly

Batteries must be charged correctly. This means you need to charge your battery with a charger that has the specified voltage and current to correctly charge your battery. You should never attempt reverse charging, since charging a battery with the polarity reversed can cause a reversal in battery polarity, causing gas pressure inside of the battery to rise, which can lead to leakage of the batteries in the pack. Also avoid overcharging. Repeated overcharging can lead to deterioration in pack performance and the battery pack may get over heated. Also note that battery charging efficiency drops at temperatures above 40°C.

Batteries have to be protected from unexpected damage

Batteries, understandably should have some basic protection everyday damage. For example the battery terminals [(+) connector and/or (-) connector] should never be touched or connected to metal wires, necklaces, or chains. Batteries should not be dropped since dropping a battery will cause the battery to malfunction or puncture. Also batteries should not be twisted or bent. Since any such forced movement will cause the battery to fail.

Batteries have to be handled safely

Furthermore batteries should never be disassembled. Batteries should never be used if an abnormality is detected such as foul odor, deformation, discoloration, bubbling and so on. Battery cells, such as Li-ion or Li-polymer cells should never be reused after removing from the chemistry from the battery pack. Also never touch any liquid coming out of the battery if there is an electrolyte leakage. Also batteries and water should never mix. Once water or moisture gets onto the battery, the battery has the potential to malfunction. In addition never store batteries in hot temperatures 140 degrees Fahrenheit or more. Furthermore do not put batteries into a fire, do not crush, puncture, or nail a battery. Finally never solder directly onto the battery casing or terminals.