General Science Archives - Get Homeschooled: Empowering Homeschooling Tips & Strategies

Battery facts Modern batteries have become amazing powerhouses for today’s portable devices. The history of batteries is a fascinating story, with men and women across the world striving to harness the remarkable properties of electricity and make them available everywhere. Just 10 years ago people were walking around with the proverbial “Brick” cell phone. However today it is now possible to lose your phone within the average pocket or smallest of handbags, this is in no small measure due to the advances in battery technology. All batteries available today have their own advantages that make them ideal for particular purposes, however, they all have an Achilles heel. Get to know the batteries and their funny little ways at Battery Facts. Battery Facts provides you with all you need to know about batteries - From how a battery works, to which battery is best for a purpose. The Development of the Battery Modern batteries have become amazing powerhouses for today’s portable devices. They have a fascinating history, with men and women across the world striving to harness the remarkable properties of electricity and make them available everywhere. Luigi Galvani 1780 (1737 - 1798) During the 1780s, biologist Luigi Galvani performed experiments at the University of Bologna involving frogs. While cutting a frog’s leg, Galvani's steel scalpel touched a brass hook that was holding the leg in place. The leg twitched. Further experiments confirmed this effect, and Galvani was convinced that he was seeing the effects of what he called animal electricity, the life force within the muscles of the frog. At the University of Pavia, Galvani's colleague Alessandro Volta was able to reproduce the results but was skeptical of Galvani's explanation. By experiment, Volta found that it was the two dissimilar metals, not the frog’s leg that produced the electricity. The frog’s leg was just an indicator of the presence of the electricity Alessandro Volta 1880 (1745-1827) One of the enthusiastic admirers of Galvani was a university professor in Padova Alessandro Guiseppe Antonio Anastasio Volta. He repeated Galvani's experiments many times with many different materials. From these experiments, he came to the conclusion that it was the two dissimilar metals, not the frog’s leg that produced the electricity. The frog’s leg was just an indicator of the presence of electricity. In 1800, after extensive experimentation, he developed the voltaic pile. The original voltaic pile consisted of a pile of zinc and silver discs and between alternating discs, a piece of cardboard that had been soaked in saltwater. A wire connecting the bottom zinc disc to the top silver disc could produce repeated sparks. No frogs were injured in the production of a voltaic pile. Volta built different piles using thirty, forty or sixty elements. This enabled him to study the action of the pile on the electric fluid, depending on the number of elements, and he confirmed that the electric shock increased in intensity with the number of elements used in the pile. If more than twenty elements were used, it became painful. The first piles constructed by Volta comprised alternating zinc and copper discs. Each was separated from its neighbour by a piece of cloth or card dampened by an acid solution. The column was supported by three vertical glass rods. William Sturgeon 1830 (1783-1850) William Sturgeon was an English electrical engineer. In 1825 he built the first practical electromagnet, in 1832 invented the commutator for electric motors and in 1836 made the first moving-coil galvanometer. A major problem with the Voltaic pile was that it could not provide current for a sustained period of time. Sturgeon worked on the problem and in 1830 produced a battery with a longer life than that of Volta by amalgamating the zinc. Contributing to the major problem with batteries was a thin film of hydrogen bubbles that formed over the positive electrode. The thin film of hydrogen caused increased internal resistance of the battery that reduced its effective electromotive force (voltage). This process of a thin film of hydrogen collecting on the electrode is known as polarization. The Volta cell had certain inherent weaknesses - any impurity in the zinc plates used caused erosion of the electrode. Sturgeon developed a long-lasting battery that consisted of a single-cell cylinder of cast iron into which a cylinder of amalgamated rolled zinc was placed. Discs of the millboard located between the cast-iron cell and the cylinder of zinc prevented contact with the different metals. Dilute sulfuric acid was used to charge the battery. John Daniell 1835 (1790-1845) John Daniell began experiments in 1835 in an attempt to improve the Voltaic battery with its problem of being unsteady and as a weak source of electrical current. His experiments soon led to remarkable results. In 1836, he invented a primary cell in which hydrogen was eliminated in the generation of electricity. Daniell had solved the problem of polarization. In his laboratory, he learned to alloy zinc with mercury. His version was the first battery that produced a constant reliable source of electrical current over a long period of time. To make the Daniell cell, a copper plate is placed at the bottom of a glass jar. Copper sulfate solution is poured over the plate to half-fill the jar. Then a zinc plate is hung in the jar as shown and a zinc sulfate solution is poured very carefully into the jar. Copper sulfate is denser than zinc sulfate, so the zinc sulfate "floats" on top of the copper sulfate. Gaston Planté 1859 (1834-1889) In 1859 Planté began experiments that resulted in the construction of a battery for the storage of electrical energy; his first model contained two sheets of lead, separated by rubber strips, rolled into a spiral, and immersed in a solution containing about 10 percent sulfuric acid. A year later he presented a battery to the Academy of Sciences consisting of nine of the elements described above, housed in a protective box with the terminals connected in parallel. His battery could deliver remarkably large currents. Initial capacity was quite limited since the positive plate had little active material available for reaction. In about 1881, Faure and others developed batteries using a paste of lead s for the positive plate active materials. This allowed a much quicker formation and better plate efficiency than the solid Planté plate. Although the rudiments of the flooded lead-acid battery date back to the 1880s, there has been a continuing stream of improvements in the materials of construction and the manufacturing and formation processes. Since many of the problems with flooded lead-acid batteries involved electrolyte leakage, many attempts have been made to eliminate free acid in the battery. Georges Leclanché 1866 (1839-1882) In 1866, Georges Leclanche patented a new system, which was immediately successful. In the space of two years, twenty thousand of his cells were being used in the telegraph system. Leclanche's original cell was assembled in a porous pot. The positive electrode consisted of crushed manganese dioxide with a little carbon mixed in. The negative pole was a zinc rod. The cathode was packed into the pot, and a carbon rod was inserted to act as a currency collector. The anode or zinc rod and the pot were then immersed in an ammonium chloride solution. The liquid acted as the electrolyte, readily seeping through the porous cup and making contact with the cathode material. Leclanche's "wet" cell (as it was popularly referred to) became the forerunner to the world's first widely used battery, the zinc-carbon cell. The Leclanche cell was used extensively for telegraphy, signaling, and electric bell work; and for most work where the intermittent current is required and where it is essential that the battery should require very little attention. The cell proved very useful in the early years of the telephone, before power was centralised in the exchanges, every telephone needed to have its own source of electricity. The battery was hidden inside a wooden box, often fixed with the telephone on the wall. It proved less suitable as conversations lengthened, and for long-distance calls. In a prolonged call, the start might be fine, but the conclusion could well be inaudible, as the battery ran down. However, the Leclanche was to some extent self re-charging, thanks to the chemicals inside it reacting with the surrounding air and before too long the telephone would be ready for action again. Carl Gassner 1887 The Leclanche cell was quite heavy and prone to breakage but steadily improved over the years. The idea of encapsulating both the negative electrode and porous pot into a zinc cup was first patented by J.A. Thiebaut in 1881. But, it was Carl Gassner of Mainz who is credited as constructing the first commercially successful "dry" cell. Variations followed. Carl Gassner patented the first "dry" cell in 1887 with zinc as the container for the other elements as well as for the negative electrode. The electrolyte was absorbed in a porous material and the cell was sealed across the top. This cell was easy to handle and portable. It became the prototype for the dry battery industry. By 1889 there were at least six well-known dry batteries in circulation. Later battery manufacturing produced smaller, lighter batteries, and the application of the tungsten filament in 1909 created the impetus to develop batteries for use in torches. Waldmar Jungner 1899 Waldmar Jungner invented the nickel-cadmium battery in 1899. At that time, the materials were expensive compared to other battery types available and its use was limited to special applications. In 1932, the active materials were deposited inside a porous nickel-plated electrode and in 1947 research began on a sealed nickel-cadmium battery. Rather than venting, the internal gases generated during the charge were recombined. These advances led to the modern sealed nickel-cadmium battery, which is in use today. Nickel-cadmium prefers fast charge to slow charge and pulse charge to DC charge. It is a strong and silent worker; hard labour poses little problem. In fact, nickel-cadmium is the only battery type that performs well under rigorous working conditions. All other chemistries prefer shallow discharge and moderate load currents. Nickel cadmium does not like to be pampered by sitting in chargers for days and being used only occasionally for brief periods. A periodic full discharge is so important that, if omitted, large crystals will form on the cell plates (also referred to as memory) and the nickel-cadmium will gradually lose its performance. Thomas Alva Edison 1903 (1847-1931) As with several of Thomas Edison’s later projects, such as his effort to mine iron ore and his quest to create synthetic rubber, his attempts at improving the battery did not lead to the results he hoped for. Edison started his work on the battery in the 1890s, just after the motor car had been introduced. At that time, the petrol engine was still unreliable, and steam and electric cars sold in larger numbers. One problem with electric cars, however, was that the lead-acid batteries that they used were extremely heavy. Another was that the acid corroded the lead inside the battery, shortening the useful life of the battery. Edison began looking for a way to make batteries lighter, more reliable, and at least three times more powerful so that they could become the basis of a successful electric car. Edison and his team conducted tests of all sorts of metals and other materials, looking for those that would work best in batteries. The tests numbered in the thousands and lasted until 1903 when he finally declared his battery finished. The battery used potassium hydroxide, which reacted with the battery’s iron and nickel electrodes to create a battery with a strong output that was reliable and rechargeable. As usual, Edison announced the new battery with great fanfare and made bold claims about its performance. Manufacturers and users of electric vehicles, which now included many urban delivery and transport trucks, began buying them. Then stories about battery failures started coming out. Many of the batteries began to leak, and others lost much of their power after a short while. The new nickel-graphite conductors were failing. Engineers who tested the batteries found that while lightweight, the new alkaline battery did not significantly outperform an ordinary lead-acid battery. Edison shut down the factory immediately, and between 1905 and 1908, the whole battery was redesigned. Edison came up with a new design, and although the new battery used more expensive materials, it had better performance and more power. By 1910, battery production was again underway at a new factory near the West Orange, NJ laboratory. However, it was too late for the electric car. Edison’s friend Henry Ford introduced the lightweight, inexpensive Model T in 1909, which helped make the petrol engine the standard for the automobile. Samuel Ruben 1930 (1900-1988) The story of Duracell begins in the early 1920s with an inventive scientist named Samuel Ruben and an eager manufacturer of tungsten filament wire named Philip Rogers Mallory. Ruben came to the P.R. Mallory Company seeking a piece of equipment he needed for an experiment. But Ruben and Mallory saw an opportunity: uniting the one's inventive genius with the other's manufacturing muscle. Their partnership, which would last until 1975 with Mallory's death, was the bedrock of Duracell International. Samuel Ruben's inventions revolutionized battery technology. Amidst World War II, for instance, Ruben devised the mercury cell, which packed more capacity in less space and was durable enough for the harsh climates of wartime theatres like North Africa and the South Pacific — places where ordinary zinc carbon batteries used in flashlights, mine detectors, and walkie-talkies couldn't hold up. P.R. Mallory manufactured millions of mercury cells for the war effort. The Mallory Battery Company was formed shortly thereafter. The mercury cell has now largely been phased out due to its environmental impact. Lewis Urry 1950 (1927-2004) Lew Urry graduated from the University of Toronto in 1950 with a Bachelor of Science degree. He got a job working for the Eveready battery division of Union Carbide in Toronto, then moved to Cleveland at the company's request in 1955, where he continued his research into creating a ‘better battery’. Lew Urry developed the small alkaline battery in 1949. The inventor was working for the Eveready Battery Co. at their research laboratory in Parma, Ohio. Alkaline batteries last five to eight times as long as zinc-carbon cells, their predecessors. Urry examined past failed attempts at creating an alkaline battery and experimented with different combinations, before discovering that powdered zinc was the best electrolyte. He changed the shape of the battery from a button to a cylinder, then gave a demonstration using toy cars in the company cafeteria. One car used the best battery at the time, carbon zinc, and the other contained his prototype. The car with the alkaline battery outperformed the other by a considerable margin. Today Most of today's exotic rechargeable battery systems--nickel-cadmium, nickel-metal hydride, and a variety of lithium-based cells--are 20th Century developments, products of research labs at major corporations and universities. New chemistries are no longer discovered through experimentation because the principles of battery design and operation are now well-known. Today new efforts in battery design focus on making the optimal chemistries work in practical cells. Battery Types There are battery technologies to suit all conditions and purposes. Modern uses may demand long life, small size, high current, lightweight or any combination of these factors and batteries have been developed to satisfy all of these needs. Take a browse through the different types of batteries and find out which is best for your needs: AAA Batteries The AAA battery (also called R03 or "triple-A"), is the smaller sister (or brother if you prefer your batteries to be male) of the AA battery. It is gaining in popularity quickly and is already the second most common battery sold in the UK. All AAA batteries share the same cylindrical shape with a height of 1.752" (44.5mm) and a diameter of 0.413" (10.5mm). Most AAA batteries use alkaline technology, with a voltage of 1.5V. The AAA battery is however also available as a rechargeable battery. The NiMH AAA rechargeable battery is rated at 1.2V but performs as well as the alkaline version in modern high-drain applications, such as digital cameras. The increased use of and demand for the AAA battery is the result of battery-powered devices becoming smaller and more efficient, while battery technology has advanced such that a current AAA battery packs as much punch as only an AA battery could deliver a few years ago. The smaller size and reduced weight are also important considerations for the designers of the newest generation of portable CD players and other gadgets. For some devices, the battery compartment and the batteries are the largest and heaviest component of the entire device! AA Batteries The AA battery (sometimes affectionately called "double-A"), is the most common battery size. Every year, about 200 million are sold in the UK alone! The AA standard actually refers to the physical dimension of the battery: cylindrical, measuring 1.988" (50mm) in height with a diameter of 0.571" (14.5mm). Amongst battery professionals, the AA battery is also called an R6. Based on this physical standard, a large number of different AA batteries have actually been developed. They differ in performance, electrical specification, and suitability for various applications. Zinc-Carbon AA batteries have been available for the longest amount of time. They are the least expensive and work well in low-drain applications, such as portable radios or torches. They don't work well when the application requires a lot of electricity quickly, because the chemicals in the battery start deteriorating, with the result of the battery losing power. Low to moderate drain applications allow the battery chemicals to recover, and thus make for a reasonable life span. Alkaline AA batteries are the best general-purpose AA battery available today. They provide more power than Zinc-Carbon AA batteries and also work much better at lower temperatures. The cheapest alkaline AA battery comes close to a Zinc-Carbon battery in price but still exceeds its performance. A top-of-the-range alkaline AA battery, such as the Duracell Ultra M3 commands a visible premium but outlasts not just Zinc-Carbon AA batteries, but also several other alkaline AA batteries by multiples. More recently lithium AA batteries have emerged to power high-drain devices, such as digital cameras. They clearly outperform any alkaline AA battery in such demanding electronic applications as digital photography, but this extra performance is also visible in their price. The most economical and environmentally friendly version of the AA battery is the NiMH rechargeable AA battery. Recharging a set of NiMH AA rechargeables costs only a small percentage of the price of alkaline AA batteries, and when you've used them, you don't have to pile your used batteries into a landfill, you simply recharge them. NiMH AA rechargeables also use less dangerous materials than the previous generation of NiCd rechargeable batteries. Rechargeable AA batteries are also typically rated at a voltage of 1.2V, rather than the 1.5V nominal voltage of the pre-charged batteries. Because of the difference in chemical process inside the battery, however, the rechargeable AA battery can still outperform an alkaline AA battery in many applications. Camcorder Batteries A battery in a camcorder has a tough life. It needs to provide a high voltage for all of the clever electronics that ensure great pictures no matter where you point the camera and also provide a strong current to drive the tape motor. This has made for pretty large camcorder batteries. There are currently three generations of camcorder batteries, all of which are still being manufactured, sold, and used: • Nickel-Cadmium (NiCd) is the best established, most common, and least expensive technology. • Nickel-Metal Hydride (NiMH) is a significant improvement over NiCd, with faster recharge times, and good performance for a much larger number of recharge cycles. A NiMH battery pack will typically have a capacity of 30%-50% over that of a NiCd battery pack of the same size. The NiCd memory effect, which reduces the efficiency of the battery pack with each charge/discharge cycle, has also been overcome in NiMH camcorder batteries. When the battery pack does eventually expire, NiMH is a lot friendlier to the environment, because it removes the Cadmium in NiCd battery packs from household waste. • Lithium-Ion (Li-Ion) technology is the most recent. It outperforms the other technologies but does so at a price. Li-Ion camcorder battery packs are also 'intelligent, in that they have on-device electronics that record usage information and allow the battery pack to be utilized more effectively than without this information. Have you ever attempted to buy a replacement camcorder battery? You'll be surprised at the price of some original brand battery packs. It is unfortunate (for the consumer) that so many camcorders each require a special battery pack that isn't compatible with any other camera or battery pack. This of course means that the maker of the camcorder is in a good position to dominate the supply and dictate the price. When you are looking for a camcorder, you have a wide choice, and manufacturers need to price the camcorders aggressively to compete with each other. Once you have your brand XXX camcorder, you'll also have to get their battery packs, so your ability to shop around has been dramatically reduced. Fortunately, a number of third-party providers have stepped in, in support of the cost-aware consumer. Uniross and Fameart are amongst the firms offering replacement camcorder battery packs for a wide variety of camcorders. Uniross is one of the leaders in rechargeable battery technology and makes very high-quality battery packs. In fact, because some of these third-party providers specialize in rechargeable batteries, their products can sometimes exceed the performance of the original battery packs, while still being less expensive. Camera Batteries Cameras tend to be used very intensively over a short amount of time and then stored for a while before their next use. This has resulted in lithium batteries dominating the market for camera batteries. Lithium batteries can provide a lot of relatively high-voltage power and do so quickly. This is important when the battery needs to power the film motor, the range finder electronics, the powered zoom and a flash, nearly all at the same time. Lithium batteries also have a shelf life of 10 years or more, which means that the battery doesn't lose any charge when it is not being used. Most of the camera batteries available today are quite mature. The most common sizes come with labels such as CR123, CR2, 2CR5 or CRP2P. All of the big brand battery manufacturers offer these batteries, although some electronics companies (such as Panasonic), and some film companies (such as Kodak) also offer photo batteries under their brand. Because of the relative maturity of this type of battery, there are only small differences in performance between the camera batteries sold with brand names you would recognize. As such, there are great opportunities to save money by shopping around. One more recent battery is the CR-V3. It is a 6 Volt lithium battery that will fit into a battery compartment the same size as two AA batteries. Because it doesn't waste the space between two cylindrical AA cells, it has more space for electricity-producing chemicals, and will thus last longer than a pair of lithium AA batteries. Digital Camera Batteries Digital Cameras place a huge burden on the batteries that provide them with power. When being used, they need a large amount of electricity very quickly. And of course, it still needs to work after a month or two of being stored. Even though some alkaline batteries have very high rated capacities (up to 2500mAh), the method by which alkaline batteries convert their chemical energy into electrical energy places a limit on how much power they can produce. This gives even the best alkaline AA batteries a run for their money in power-hungry digital cameras. Rechargeable batteries fare much better. The current technology used in rechargeable batteries for digital cameras uses Nickel-Metal-Hydride (NiMH) chemistry to convert the stored chemical energy into electricity. This chemical process can generate electricity far more rapidly, and will thus allow a 2100mAh NiMH battery to outperform a 2500mAh alkaline battery in a digital camera. Current NiMH technology has a number of additional advantages over its predecessor, Nickel-Cadmium or NiCd. NiCd rechargeable batteries suffer from something called a ‘memory effect'. This reduces the amount of electricity that the battery can store in each charge/discharge cycle. Not by a great deal for each cycle, but over time you would notice that you got even fewer pictures from your digital camera before you had to stop to recharge. One disadvantage that rechargeable batteries for digital cameras have not overcome is the loss of stored power while not in use. A rechargeable battery loses 1-3% of its power EVERY DAY when not in use. If you are running a professional photo studio, that won't be an issue because you're recharging every day anyway. But for a more casual user, quickly grabbing the camera on the way to the car for a long weekend can often result in a surprise – and no pictures! Fortunately, most digital cameras are designed to also work with lithium batteries. These typically come in the same size as AA alkaline batteries but are much better at keeping up with a digital camera's voracious appetite for power. They also have shelf lives of 10 years or more. The ideal strategy will be to rely on rechargeable batteries for most of the time but to keep a spare set of lithium batteries handy for emergency use. Hearing Aid Batteries Hearing aids are designed to be small and light so that they can be worn behind, or even in the ear. Of course, they still need a suitable source of electricity to function. Hearing aid batteries have thus been optimized to be small and light. The battery technology best suited to produce light batteries is the zinc-air battery. Out of all of the battery chemicals commonly in use today, it allows for the greatest amount of power to be stored for a given weight. This is a function of using air (or more precisely the oxygen in the air) as part of the chemical process to produce electricity. Because no storage is required for this chemical inside the battery, it can be made lighter. This unique technology brings a few features of its own. Zinc-air batteries that are sealed when manufactured. While sealed, they have an exceptionally long shelf life. To use a zinc-air battery, you have to remove the sealing tab from tiny holes on the battery to let in air. This starts the electricity-producing chemical reaction. The way this chemical process proceeds makes it ideal to provide a steady current over a period of time. Zinc-air batteries are not good at producing peak power quickly in a high-drain application (e.g. a camera), because of the steady rate of the chemical process. In hearing aids, this steady discharge is exactly what's required, however. Because the chemical process continues even when the battery is not used to power a device, the shelf life of a zinc-air battery once un-sealed is quite limited. Li-ion Batteries • Very good power-to-weight ratio • Found in high-end laptop computers and cellular phones • Now taking market share away from NiMH • Outputs 3v per cell therefore NOT directly interchangeable with normal 1.5v batteries. (sold as a unit that replaces 2, 1.5v batteries) • Made from layered sheets of aluminum foil coated with cobalt oxide, which acts as the cathode with the anode made from a thin copper sheet coated with carbon materials. • The thin film cathode and anode are separated by a sheet of plastic, rolled up together in a spiral, and immersed in a liquid electrolyte medium of Lithium. • These batteries produce the same energy as NiMH batteries but are 40% smaller, half the weight, and are better for the environment because they don't contain toxic materials such as cadmium or mercury. • Currently more expensive than a comparable NiMH battery. • There are safety issues when charging - Ensure Li-ion batteries are only charged using a battery charger specifically built for the purpose. NiCad Batteries • Enabled the early use of portable power tools, camcorders, laptop computers, and cellular phones. • Was the industry standard for portable computers until 1992. • NiCad batteries have been virtually displaced by NiMH and Li-ion. • Low energy density by weight makes it less desirable for portable computers. • NiCad batteries have a memory that prevents efficient topping up. • NiCads pollute the environment if not disposed of correctly. • Low cost and high power capability make it the best technology for motor-driven portable devices such as power tools. • Uses nickel hydroxide and cadmium electrodes with potassium hydroxide as the electrolyte. NiMH Batteries • Introduced in 1990 • Rapidly took market share away from NiCd batteries in the portable computing industry • Differ from NiCd only by their negative electrode which is made of a metal alloy capable of storing a large number of electrons. • Metal hydride is produced as the charging product • Energy density is almost 50% greater than NiCad Rechargeable Batteries Rechargeable batteries do exactly what the name implies. Once you've used them, you don't dispose of the battery, you simply recharge it! Like primary batteries, rechargeable batteries have four basic components - a positive electrode (cathode), a negative electrode (anode), a separator and electrolytes. But that's where the similarities end. The chemicals inside a rechargeable battery are reversible, allowing them to be recharged again and again. For heavy users of batteries, rechargeable batteries have always been a cheaper source of electricity. Recharging 4 batteries from mains electricity costs about 2p, whereas a new set of alkaline batteries can easily cost £4.00 or more. You don't have to be a rocket scientist to realize that the slightly higher cost of buying rechargeable batteries is more than covered by savings over the life of a set of rechargeable batteries. With high-performance rechargeable batteries, you can go through 1000 charge/discharge cycles before you need to replace them. That means literally hundreds of pounds saved over the use of primary batteries. A further important consideration is how battery use affects the environment. Using rechargeable batteries reduces household waste. 15 billion ordinary batteries are thrown away every year, all of which end up in landfill sites. Rechargeable batteries can be reused which helps reduce the impact disposable batteries have on the environment. Rechargeable batteries have been continuously enhanced to improve performance, as well as becoming more environmentally friendly. The most ecological rechargeable batteries are Ni-MH rechargeable units (Nickel-metal hydride), which are the current state-of-the-art in rechargeable battery technology. The previous generation's technology, Nickel-Cadmium, is still in use, being manufactured and sold. However, Ni-MH technology is superior in several ways: • Ni-MH rechargeable batteries do not suffer from the Ni-Cd ‘memory effect', thus allowing a far greater number of charge/discharge cycles before the rechargeable battery's performance declines. • Ni-MH technology is more environmentally friendly because it avoids introducing highly toxic Cadmium from Ni-Cd cells into household waste. Rechargeable batteries are ideal for high-drain devices that use a lot of power, such as digital cameras or camcorders. But they should never be used in smoke detectors and won't work that well in other low-drain devices. Here's why: Primary batteries have a much greater ability to retain their charge when not used, or when only a trickle charge is drawn from the battery. But rechargeable batteries lose some of their power every day, whether they are in a device or not. Watch Batteries As in many other aspects of life, for watch batteries size matters. They come in about 60 different sizes but are all button cells and designed to pack as much energy as possible into the smallest space possible. Current watch batteries nearly all use silver oxide battery technology because that is most efficient when squeezing the last bit of electricity into a confined space for storage. This also means that watch batteries are all rated at 1.55V and differ primarily in their physical dimensions. Of course, a large watch battery will also be able to store more electricity, and will thus be rated at a higher capacity. Over time, the watch industry has added new features such as background lighting or audible alarms to watches. Some even feature calculators, digital diaries or other functions. This has led to the development of additional 'high drain' versions of watch batteries to feed the extra requirement for power. In the IEC 'standard' battery designation convention, the low drain or normal version of the watch battery will end with the letter 'W', while the high drain version would end in 'SW'. A common watch battery is the SR44W (or the SR44SW for the high-drain version). Because both versions have the same voltage and the same physical dimensions, it is perfectly safe to use the high-drain version instead of the regular version. Using the regular battery in a high-drain watch will however mean that you'll have to change the battery much earlier. This interchangeability has actually led a number of watch battery manufacturers to drop the low-drain version, and only produce the high-drain version. When replacing your watch battery, it is useful to know that there isn't a reason for an alarm when you're fitting a battery that has a different designation, just because you are upgrading to the high-drain version. Until a few years ago, several watch batteries used mercury technology. This has now been phased out for environmental reasons. Mercury is highly toxic, and there is no reasonable way to safely extract and recycle mercury in watch batteries. For most watches, there will be a suitable replacement battery that uses silver oxide technology with the same physical dimensions. Mercury button cells did however operate with a nominal 1.35V, rather than the 1.55V of a silver oxide watch battery. Zinc-Air Batteries • Rechargeable zinc air has emerged from its research and development phase and is now in the early stages of commercialization. • Differs from other rechargeable battery systems by extracting oxygen molecules required for electricity-producing chemical reactions directly from the air. • The air electrode absorbs oxygen to generate electrical current on discharge and expels oxygen during battery recharge. • On discharge, oxygen is brought into the cell, so there's no need to enclose a heavy metal oxidizer. • Runtime exceeds other types by far • Higher energy density, power output, and less charge time than any other battery. • Able to power a laptop computer for over 8 hours. Battery Labels There is no universal standard for labelling batteries. This is a continuous source of confusion for consumers looking to replace a battery. Most manufacturers use their own labelling or designation system, which sometimes is similar to others, but not necessarily. The International Electrotechnical Commission (IEC, http://www.iec.ch/) has proposed a standard battery designation system that provides at least some clues as to which batteries it refers to. There are two variants of this standard: Variant 1 The battery designation has five elements: 1. One digit for the number of cells connected in series. 2. One letter to denote the electrochemical system. 3. One letter to denote shape (R=Round, P=Not Round). 4. Two or three digits as a unique physical dimension designation. 5. One or two letters as designation modifiers. The electrochemical system is identified by the following: L - 'Alkaline' S - 'Silver Oxide' C - 'Lithium/MnO2' B - 'Lithium/CF' For example, an 'LR44' cell uses alkaline technology (L), is round (R), and has a unique dimension identifier of 44 (11.6mm diameter, 5.4mm height). Or an 'SR44W', which uses silver oxide technology (S), is also round (R), has the same physical dimensions (44), and a modifier of 'W' to denote the 'high drain' variant, as opposed to the SR44SW which is the 'low drain' variant. Variant 2 The battery designation is as above, except that the physical dimension designation (element 4) is replaced by: 4a. Two-digit code denoting the maximum diameter. 4b. Two-digit code denoting the maximum height. For example, a 'CR2032' cell uses Lithium/MnO2 technology (C), is round (R), has a maximum diameter of 20mm (20), and a maximum height of 3.2mm (32). As indicated, not everyone sticks to these standards. The CR2032 cell is also called a DL2032 (by Duracell, no less). The SR44W has many names, including '357', 'V357', 'D357H', '228', 'J', '280-62', 'SB-B9', 'SR1154' and probably others. Competent battery suppliers (such as Battery Force at http://www.battery-force.co.uk) make finding the right battery a lot easier by maintaining cross-reference databases of all of the various codes a particular battery can have. Battery Data Cell Type Shape Height Diameter AAAA Cylindrical 42.5mm 8.3mm AAA Cylindrical 44.5mm 10.5mm AA Cylindrical 50.5mm 14.5mm C Cylindrical 50.0mm 26.2mm D Cylindrical 61.5mm 34.2mm J Rectangular 48.5mm 33.5 x 9.2 mm N Cylindrical 29.35mm 11.95mm 9-volt Rectangular 48.5mm 26.5 x 17.5mm