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Q: How is the Right Battery Chosen for Portable Computing

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Q: How does Cycling Affect Battery Performance?

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Q: How is the right battery chosen for wireless applications?

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 (April 2004) Q: How Can Lead-acid batteries be restored and have prolonged life?

The sealed Lead-acid battery is designed with a low over-Voltage potential to prohibit the battery from reaching its gas-generating state during charge. This prevents water depletion of the sealed system. Consequently, these batteries will never get fully charged and some sulfation will develop over time.

Finding the ideal charge Voltage threshold is critical and any level is a compromise. A Voltage limit above 2.40 Volts per cell produces good battery performance but shortens the service life due to grid corrosion on the positive plate. The corrosion is permanent. A Voltage below the 2.40V/cell threshold strains the battery less but the capacity is low and sulfation sets in over time on the negative plate.

Driven by diverse applications, two sealed Lead-acid types have emerged. They are the sealed lead-acid (SLA), and the valve regulated Lead-acid (VRLA). Technically, both batteries are the same. Engineers may argue that the word ‘sealed Lead-acid’ is a misnomer because no Lead-acid battery can be totally sealed.

The SLA has a typical capacity range of 0.2Ah to 30Ah and powers personal UPS units, local emergency lighting and wheelchairs. The VRLA battery is used for large stationary applications for power backup. We are looking at methods to restore and prolong these two battery systems separately.

The sealed Lead-acid (SLA)

SLA batteries with mild sulfation can be restored but the work is time consuming and the results are mixed. Reasonably good results are achieved by applying a charge on top of a charge. This is done by fully charging an SLA battery, then removing it for a 24 to 48 hour rest period and applying a charge again The process is repeated several times and the capacity is checked with a final full discharge and recharge.

Another method of improving performance is by applying an equalizing charge, in which the charge Voltage threshold is increased by about 100mV, typically from 2.40V to 2.50V. This procedure should last no longer than one to two hours and must be carried out at moderate room temperature. A careless equalize charge could cause the cells to heat up and induce venting due to excessive pressure. Observe the battery during the service.  

The cylindrical SLA, made by Hawker and sold under the Cyclone name, requires slightly higher Voltages to reverse sulfation. An adjustable power supply works best for the service. Set the current limit to the lowest practical setting and observe the battery Voltage and temperature during charge. Initially, the cell Voltage may rise to 5V, absorbing only a small amount of current. In about two hours, the small charging current converts the large sulfate crystals back into active material. The internal cell resistance decreases and the cell starts to clamp the Voltage. At around 2.30V, the cell accepts charge. If the sulfation is advanced, this remedy does not work and the cell needs replacing.

Sealed Lead-acid batteries are commonly rated at a 20-hour discharge. Even at such a slow rate, a capacity of 100% is difficult to achieve. For practical reasons, most battery analyzers use a 5-hour discharge when servicing these batteries. This produces 80% to 90% of the rated capacity. SLA batteries are normally overrated and manufacturers are aware of this practice.

Cycling an SLA on a battery analyzer may provide capacity readings that decrease with each additional cycle. A battery may start off at a marginal 88%, then go to 86%, 84% and 83%. This phenomenon can be corrected by increasing the charge Voltage threshold from 2.40V to 2.45V and perhaps even 2.50V. Always consider the manufacturer’s recommended settings. Cyclone batteries require slightly higher Voltage settings than the plastic version.

Avoid setting the charge Voltage threshold too high. In an extreme case, the limiting Voltage may never be reached, especially when charging at elevated temperatures. The battery continues charging at full current and the pack gets hot. Heat lowers the battery Voltage and works against a further Voltage raise. If no temperature sensing is available to terminate the charge, a thermal runaway can be the result.

The recovery rate of SLA batteries is a low 15%. Other than reverse sulfation, there is little one can do to improve SLA. Because the SLA has a relatively short cycle life, many fail due to wear-out.

Valve regulated Lead-acid (VRLA)

The charge Voltage setting on VRLA is generally lower than SLA. Heat is a killer of VRLA. Many stationary batteries are kept in shelters with no air conditioning. Every 8°C (15°F) rise in temperature cuts the battery life in half. A VRLA battery, which would last for 10 years at 25°C (77°F), will only be good for 5 years if operated at 33°C (95°F). Once damaged by heat, no remedy exists to improve capacity.

The cell Voltages of a VRLA battery must be harmonized as close as possible. Applying an equalizing charge every 6 months brings all cells to similar Voltage levels. This is done by increasing the cell voltage to 2.50V/cell for about 2 hours. During the service, the battery must be kept cool and careful observation is needed. Limit cell venting. Most VRLA vent at 0.3 Bar (5 psi). Not only does escaping hydrogen deplete the electrolyte, it is highly flammable.

Water permeation, or loss of electrolyte, is a concern with sealed Lead-acid batteries. Adding water may help to restore capacity but a long-term fix is uncertain. The battery becomes unreliable and requires high maintenance.

Simple Guidelines

Always store Lead-acid in a charged condition. Never let the open cell Voltage drop much below 2.10V. Apply a topping charge every six months or when recommended.

·     Avoid repeated deep discharges. Charge more often or use a larger battery.

Prevent sulfation and grid corrosion by choosing the correct charge and float Voltages.

Avoid operating Lead-acid at elevated ambient temperatures.

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(Febuary 2004)Is Memory a Myth or a Fact?

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 ( January 2004) Non-Correctable Battery Problems. Some rechargeable batteries can be restored through external means, such as applying a full discharge.

(December 2003) Q: Is the runtime of a portable device directly related to the size of the battery?

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(November 2003) Do and don't battery table

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(October ,2003)Recycling batteries

Modern batteries are often promoted on their environmental qualities. Lithium-based batteries fall into this category. While Nickel-cadmium presents an environmental problem on careless disposal, this chemistry continues to hold an important position among rechargeable batteries. Power tools are almost exclusively powered by Nickel-cadmium. Lead-acid batteries continue to service designated market niches and these batteries also need to be disposed of in a proper manner. Lithium-ion would simply be too fragile to replace many of these older, but environmentally unfriendly, battery chemistries.

Our quest for portability and mobility is steadily growing, so is the demand for batteries. Where will the mountains of batteries go when spent? The answer is recycling.

The lead acid battery has led the way in recycling. The automotive industry should be given credit in organizing ways to dispose of spent car batteries. In the USA, 98% of all lead acid batteries are recycled. In comparison, only one in six households in North America recycle batteries.

Careless disposal of Nickel-cadmium is hazardous to the environment. If used in landfills, the cadmium will eventually dissolve itself and the toxic substance can seep into the water supply, causing serious health problems. Our oceans are already beginning to show traces of cadmium (along with aspirin, penicillin and antidepressants) but the source of the contamination is unknown.

Although Nickel-metal-hydride is considered environmentally friendly, this chemistry is also being recycled. The main derivative is nickel, which is considered semi-toxic. Nickel-metal-hydride also contains electrolyte that, in large amounts, is hazardous. If no disposal service is available in an area, individual Nickel-metal-hydride batteries can be discarded with other household wastes. If ten or more batteries are accumulated, the user should consider disposing of these packs in a secure waste landfill.

Lithium (metal) batteries contain no toxic metals, however, there is the possibility of fire if the metallic lithium is exposed to moisture while the cells are corroding. Most lithium batteries are non-rechargeable and are used in cameras, hearing aids and defense applications. For proper disposal, the batteries must first be fully discharged to consume the metallic lithium content.

Lithiumion batteries used for cell phones and laptops do not contain metallic lithium and the disposal problem does not exist. Most lithium systems contain toxic and flammable electrolyte.

In 1994, the Rechargeable Battery Recycling Corporation (RBRC) was founded to promote recycling of rechargeable batteries in North America. RBRC is a non-profit organization that collects batteries from consumers and businesses and sends them to recycling organizations. Inmetco and Toxco are among the best-known recycling companies in North America

Europe and Asia have had programs to recycle spent batteries for many years. Sony and Sumitomo Metal in Japan have developed a technology to recycle cobalt and other precious metals from spent Lithiumion batteries.

Battery recycling plants require that the batteries be sorted according to chemistries. Some sorting must be done prior to the battery arriving at the recycling plants. Nickel-cadmium, Nickel-metal-hydride, Lithiumion and lead acid are placed in designated boxes at the collection point. Battery recyclers claim that if a steady stream of batteries, sorted by chemistry, were available at no charge, recycling would be profitable. But preparation and transportation add to the cost.

The recycling process starts by removing the combustible material, such as plastics and insulation, with a gas fired thermal oxidizer. Gases from the thermal oxidizer are sent to the plant's scrubber where they are neutralized to remove pollutants. The process leaves the clean, naked cells, which contain valuable metal content.

The cells are then chopped into small pieces, which are heated until the metal liquefies. Non-metallic substances are burned off; leaving a black slag on top that is removed with a slag arm. The different alloys settle according to their weights and are skimmed off like cream from raw milk.

Cadmium is relatively light and vaporizes at high temperatures. In a process that appears like a pan boiling over, a fan blows the cadmium vapor into a large tube, which is cooled with water mist. This causes the vapors to condense and produces cadmium that is 99.95 percent pure.

Some recyclers do not separate the metals on site but pour the liquid metals directly into what the industry refers to as `pigs' (65 pounds) or `hogs' (2000 pounds). The pigs and hogs are then shipped to metal recovery plants. Here, the material is used to produce nickel, chromium and iron re-melt alloy for the manufacturing of stainless steel and other high-end products.

Current battery recycling methods requires a high amount of energy. It takes six to ten times the amount of energy to reclaim metals from recycled batteries than it would through other means.

Who pays for the recycling of batteries? Participating countries impose their own rules in making recycling feasible. In North America, some recycling plants bill on weight. The rates vary according to chemistry. Systems that yield high metal retrieval rates are priced lower than those, which produce less valuable metals.

Nickel-metal-hydride yields the best return. It produces enough nickel to pay for the process. The highest recycling fees apply to Nickel-cadmium and Lithiumion because the demand for cadmium is low and Lithiumion contains little retrievable metal.

Not all countries base the cost of recycling on the battery chemistry; some put it on tonnage alone. The flat cost to recycle batteries is about $1,000 to $2,000US per ton. Europe hopes to achieve a cost per ton of $300US. Ideally, this would include transportation, however, moving the goods is expected to double the overall cost. For this reason, Europe sets up several smaller processing locations in strategic geographic locations.

Significant subsidies are sill required from manufacturers, agencies and governments to support the battery recycling programs. This funding is in the form of a tax added to each manufactured cell. RBRC is financed by such a scheme.

Important: Under no circumstances should batteries be incinerated as this can cause explosion. If skin is exposed to electrolyte, flush with water immediately. If eye exposure occurs, flush with water for 15 minutes and consult a physician immediately.

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(September,03)Storing and priming of batteries Batteries are perishable products that start deteriorating right from the moment they leave the factory.

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(August,03) Q: What is the 'smart' battery

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(July,03) What is a `smart' battery? The battery has the inherit problem of not being able to communicate with the user. Neither weight, color, nor size provides an indication of the battery's state-of-charge (SoC) and state-of-health (SoH). The user is at the mercy of the battery.

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(June,02) Q: What are important considerations in discharge methods?

The purpose of a battery is to store energy and release it at the appropriate time in a controlled manner.

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(July,02)Q: Is the Lithium-ion the ideal battery?

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(May 2003)Q: What are considerations for discharging at high and low temperature. Batteries function best at room temperature. Operating batteries at an elevated temperature dramatically shortens their life.

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(April 2003) Advancements in battery rapid-testing. How accurate is AC conductance?

Not just a concept to provide greater information about battery charge conditions, Electrochemical Impedance Spectroscopy (EIS) now provides data to show superior performance. The electrochemical characteristics of a battery are determined by applying an AC potential at varying frequencies and measuring the current response of the electrochemical cell. Written by our Expert, Isidor Buchmann

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(April 2003) Q: What factors affect Charging at high and low temperatures?

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Q:What’s the role of the Supercapacitor?

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Q: Will the reusable Alkaline battery have a future?

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Q? Can the Lead-acid battery compete in modern times?

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(July 2002) Q: What are the chraracteristics of Nickel-based batteries, its dominance and the future?

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(May 2002) Q: What’s the best battery?

Battery novices often brag about phantom battery systems that offer very high energy densities, deliver 1000 charge/discharge cycles and are paper-thin. These attributes are indeed achievable but not on the same battery pack.

A certain battery may be designed for small size and long runtime, but this pack has a limited cycle life. Another battery may be built for durability but is big and bulky. A third pack may have high energy density and long durability but is too expensive for the commercial consumer.

Battery manufacturers are aware of customer needs and offer packs that best suit the application. The cell phone industry is an example of this clever adaptation. Here, small size and high energy density reign in favor of longevity. Short service life is not an issue because a device is replaced before the battery fails.

Let’s briefly examine various battery designs. A prismatic Nickel-metal-hydride battery is made for slim geometry. Its energy density is a meager 60Wh/kg and the cycle count is limited to around 300. In comparison, a cylindrical Nickel-metal-hydride offers 80Wh/kg and higher. Still, the cycle count is moderate to low. High durability Nickel-metal-hydride for industrial use and electric vehicles is packaged in large cylindrical cells. Surprisingly, the energy density on these cells is a modest 70Wh/kg.

Similarly, Lithium-ion batteries for defense applications are being produced that far exceed the energy density of the commercial equivalent. These super-high capacity Lithium-ion batteries are not approved for the commercial market for safety reasons.

Let’s examine the strength and limitations of today’s popular battery systems. Although energy density is paramount, other viral attributes are service life, load characteristics, maintenance requirements, self-discharge and operational costs. Since Nickel-cadmium remains a standard against which batteries are compared, we evaluate alternative chemistries against this classic battery type.

· Nickel-cadmium — mature but has moderate energy density. Nickel-cadmium is used where long life, high discharge rate and a extended temperature range are important. Main applications are two-way radios, biomedical equipment and power tools. Nickel-cadmium contains toxic metals.

· Nickel-metal-hydride — has a higher energy density compared to Nickel-cadmium at the expense of reduced cycle life. There are no toxic metals. Applications include mobile phones and laptop computers.

· Lead-acid — most economical for larger power applications where weight is of little concern. This battery is the preferred choice for hospital equipment, wheelchairs, emergency lighting and UPS systems.

· Lithium-ion — fastest growing battery system; offers high-energy density and low weight. Protection circuits are needed to limit Voltage and current for safety reasons. Applications include notebook computers and cell phones.

· Lithium-ion-polymer — Similar to Lithium-ion, this system enables slim geometry and simple packaging at the expense of higher cost per Watt/hours. Main applications are cell phones.

· Reusable Alkaline — Its limited cycle life and low load current is compensated by long shelf life, making this battery ideal for portable entertainment devices and flashlights.

Table 1 on page 13 summarizes the characteristics of the common batteries. The figures are based on average ratings at time of publication. Note that Nickel-cadmium has the shortest charge time, delivers the highest load current and offers the lowest overall cost-per-cycle but needs regular maintenance.

In subsequent columns I will describe the strength and limitation of each chemistry in more detail. We will also examine charging techniques and explore methods to get the most of these batteries.

Table 1:  Characteristics of commonly used rechargeable batteries.

                                                     Nickel-     Nickel-metal-     Lead-acid     Lithiumion     Lithiumion-   Rusable

cadmium          hydride                                     polymer                                     Alkaline                                                                                                               

Gravimetric Energy Density    45-80       60-120               30-50        110-160           100-130     80(initial)                                        (Wh/kg)

Internal Resistance (includes 100 to 2001    00 to 3001                      <1001        150 to 2501     200 to 3001     200 to 20001

peripheral circuits) in mW             6V pack        6V pack            12V pack       7.2V pack       7.2V pack         6V pack

Cycle Life                                          15002             300 to 5002,3             200 to 3002     300 to 5003     300 to 500             503     

(to 80% of initial capacity)                                                                                                                                  (to 50% capacity)

Fast Charge Time                        1h typical       2 to 4h                8 to 16h            2 to 4h       2 to 4h                   2 to 3h

Overcharge Tolerance              moderate         low                       high                very low         low                 moderate

Self-discharge/Month                      20%4          30%4                     5%                    10%5        ~10%5                    0.3%

(room temperature)        

Cell Voltage (nominal)                       1.25V6            1.25V6               2V                       3.6V          3.6V                    1.5V

Load Current   peak                             20C                   5C                   5C7                   >2C         >2C                    0.5C

                            best result                    1C            0.5C or lower       0.2C          1C or lower  1C or lower   0.2C or lower

Operating Temperature8                    -40 to              -20 to                -20 to                 -20 to          0 to                    0 to

                        (discharge only)             60°C               60°C                 60°C                   60°C        60°C                 65°C

Maintenance Requirement    30 to 60 days   60 to 90 days  3 to 6 months9   not required  not required.  not required

Typical Battery Cost10                           $50                  $60                   $25                   $100           $100                   $5

              (US$, reference only)             (7.2V)              (7.2V)                 (6V)                  (7.2V)           (7.2V)                (9V)

Cost per Cycle (US$)11     $0.04     $0.12     $0.10     $0.14     $0.29     $0.10-0.50

Commercial use since                         1950               1990                 1970                  1991           1999                     1992

Notes:

1 Internal resistance of a battery pack varies with cell rating, type of protection circuit and number of cells. Protection          circuit of Lithiumion and Lithium-ion-polymer adds about 100mW.

2 Cycle life is based on a battery receiving regular maintenance. Failing to apply periodic full discharge cycles may reduce the cycle life by a factor of three.

3 Cycle life is based on the depth of discharge. Shallow discharges provide more cycles than deep discharges.

4 The discharge is highest immediately after charge, and then tapers off. The capacity of Nickel-cadmium decreases 10% in the first 24h, then declines about 10% every 30 days thereafter. Self-discharge increases with higher temperature.

5. Internal protection circuits typically consume 3% of the stored energy per month.

6 1.25V is the open cell Voltage. 1.2V is commonly used as a method of rating.

7 Capable of high current pulses.

8 Applies to discharge only; charge temperature range is more confined.

9 Maintenance may be in the form of ‘equalizing’ or ‘topping’ charge.

10 Cost of battery for commercially available portable devices.

11 Derived from the battery price divided by cycle life. Does not include the cost of electricity and chargers.   

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(April 2002) Q: When was the battery invented?

One of the most important discoveries in the last 400 years has been electricity. You may ask, “Has electricity been around that long?” The answer is yes, and perhaps much longer. But electricity only became useful in the late 1800s.

The earliest methods of generating electricity were by creating a static charge. Alessandro Volta (1745-1827) invented the so-called “electric pistol” by which an electrical wire was placed in a jar filled with methane gas. By sending an electrical spark through the wire, the jar would explode.

Volta then thought of using this invention to provide long distance communications, albeit only one Boolean bit. An iron wire supported by wooden poles was to be strung from Como to Milan, Italy. At the receiving end, the wire would terminate in a jar filled with methane gas. On command, an electrical spark would be sent by wire that would cause a detonation to signal a coded event. This communications link was never built.

The next stage of generating electricity was through electrolysis. Volta discovered in 1800 that a continuous flow of electrical force was possible when using certain fluids as conductors to promote a chemical reaction between metals. Volta discovered further that the Voltage would increase when Voltaic cells were stacked. This led to the invention of the battery.

No longer were experiments limited to a brief display of sparks that lasted a fraction of a second. A seemingly endless stream of electric current was now available.

At this time, France was approaching the height of scientific advancements and new ideas were welcomed with open arms to support the political agenda. By invitation, Volta addressed the Institute of France in a series of lectures in which Napoleon Bonaparte was present. Napoleon himself helped with the experiments, drawing sparks from the battery, melting a steel wire, discharging an electric pistol and decomposing water into its elements. New discoveries were made when Sir Humphry Davy installed the largest and most powerful electric battery in the vaults of the Royal Institution of London. He connected the battery to charcoal electrodes and produced the first electric light. As reported by witnesses, his Voltaic arc lamp produced “the most brilliant ascending arch of light ever seen.” In 1802, Dr. William Cruickshank designed the first electric battery capable of mass production. Cruickshank arranged square sheets of copper soldered at their ends, intermixed with sheets of zinc of equal size. These sheets were placed into a long rectangular wooden box that was sealed with cement. Grooves in the box held the metal plates in position. The box was filled with an electrolyte of brine, or watered down acid.

Until now, all batteries were primary cells, meaning that they could not be recharged. In 1859, the French physicist Gaston Planté invented the first rechargeable battery. This secondary battery was based on Lead-acid chemistry, a system that is still used today.

The third method of generating electricity was discovered relatively late — electricity through magnetism. In 1820, André-Marie Ampère (1775-1836) had noticed that wires carrying an electric current were at times attracted to one another, while at other times they were repelled. In 1831, Michael Faraday (1791-1867) demonstrated how a copper disc was able to provide a constant flow of electricity when revolved in a strong magnetic field. Faraday and his research team succeeded in generating an endless electrical force as long as the movement between a coil and magnet continued.

In 1899, Waldmar Jungner from Sweden invented the Nickel-cadmium battery. In 1947, Neumann succeeded in completely sealing the cell. These advances led to the modern sealed Nickel-cadmium battery.

Research of the NiMH system started in the 1970s, but the metal hydride alloys were unstable in the cell environment. New hydride alloys were developed in the 1980s that improved the stability. NiMH became commercially available in the 1990s.

The first primary Lithium batteries appeared in early 1970s. Attempts to develop rechargeable lithium batteries followed in the 1980s but failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, the Lithium ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first Lithium-ion battery.

As awkward and unreliable the early batteries may have been, our descendants may one day look at today’s technology in a similar way to how we view our predecessors’ clumsy experiments of 200 years ago.  History of Battery Development

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The 88-page first edition book appeared in 1997 and covered such topics as the memory effect of Nickel-cadmium batteries and how to restore them. Some readers commented that I favored the Nickel-cadmium over the Nickel-metal-hydride. Perhaps this observation is valid and I have taken note. Having been active in the mobile radio industry for many years, much emphasis is placed on battery longevity, a quality that is true of the Nickel-cadmium. Today’s battery users prefer small size and maximum runtime. Longevity is less important, especially in the consumer market.

The second edition Batteries in a Portable World was published in 2001. With 18 Chapters and 300 pages, this book has been extended to answer most questions battery users would ask. Much emphasis is placed on new battery technologies and their field applications.

In May 2001, I created the Battery Information Website www.buchmann.ca and made the contents of the book available to everyone. New battery articles have also been added. A search engine helps the readers in finding issues of interest.

Out of sheer curiosity, I did a statistical analysis at the end of the year to find out which battery topics are being requested most often. The five winning chapters are:

Number 1. Getting the Most from your Batteries  Chapter 10

Number 2. Proper Charge Methods Chapter 4

Number 3. Internal Battery Resistance  Chapter 9

Number 4. Choosing the Right Battery Chapter 8

Number 5. The ‘Smart’ Battery Chapter 7

With “Getting the Most from your Batteries” as first choice, it is evident that people want good runtime and dependable service. “Proper Charge Methods” is also very much in the hearts of the battery users. A surprise was “Internal Battery Resistance” in third position. This subject is of growing concern with digital equipment that puts high demands on the battery. A seemingly good battery often fails to deliver the heavy current bursts because of elevated internal resistance caused by aging and high cycle count.

Batteries in a Portable World is written for the non-engineer. It addresses the use of the battery in the hands of the general public, far removed from the protected test lab environment of the manufacturer. Some information contained in this book was obtained through tests performed in Cadex laboratories; other knowledge was gathered by simply talking to diverse groups of battery users. Not all views and opinions expressed in the book are based on scientific facts. Rather, they follow opinions of the general public, who use batteries. Some difference of opinion with the reader cannot be avoided. I will accept the blame for any discrepancies, if justified.

The monthly columns, which will appear in Batteries Digest Newsletter, will be based on the book, Batteries in a Portable World. I will address such issues as the choice of battery chemistries, physical battery packs, charge and discharge methods, runtime concerns, the ‘smart’ battery, internal battery resistance and much more. I hope you will find these columns helpful.

About the Author

Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver BC. Mr. Buchmann has a background in radio communications and has studied the behavior of rechargeable batteries in practical, everyday applications for two decade