Reference Library (Articles)

House of Batteries has signed an agreement with Avnet Electronics to be their only supplier of batteries and custom battery packs for world wide sales. Avnet is the largest electronics distributor in the world. They have 43 branches and 400 outside sales people in the US alone. We are very excited about this relationship and expect it should expand our sales into many new markets and customers.

GSA Schedule Award, House of Batteries has successfully negotiated with the Government Service Administration to obtain a GSA Schedule and has a presence on the GSA Advantage website for all of our off the shelf batteries for sales to the Government entities that buy products through this channel.

Company is the only battery assembler to receive "Outstanding Provider" Award

ORLANDO, FL – House of Batteries (HOB) of Fountain Valley, CA, the largest certified woman-owned battery company in the U.S., was the only custom battery assembler to be recognized by Lockheed Martin (NYSE: LMT) as an Outstanding Small Business Provider (OSBP) for 2006 during Lockheed’s OSBP awards ceremony March 26, 2007, in Orlando, FL.

Each year, Lockheed Martin Missiles and Fire Control and Lockheed Martin Simulation Training & Support select small businesses that have consistently provided outstanding support and products. Only a select few from thousands of Lockheed Martin suppliers nationwide are recognized for superior quality in goods and service.

At a March 26, 2007 awards banquet in Orlando, executives from Lockheed Martin Missiles and Fire Control and Lockheed Martin Simulation, Training and Support presented awards to 15 companies, with House of Batteries the only battery supplier to receive the OSBP.

“Small business partners such as House of Batteries bring a unique skill set to our products and services,” said Dale Bennett, president of Lockheed Martin Simulation, Training & Support. “We have developed a long and valuable relationship with them and take pride in recognizing the significant role they play in our success.”

“We are very proud of this award,” said Maggie West, CEO of HOB. “It is testament to our intense focus on quality, engineering expertise and world class process control in every aspect of our battery assembly operations. This benefits all our customers and is especially critical for valued partners such as Lockheed Martin.”

Headquartered in Bethesda, Md., Lockheed Martin employs 140,000 people worldwide and is engaged in the research, design, development, manufacture, and integration of advanced technology systems.

HOB is the largest woman-owned battery distributor and assembler in the U.S and is an authorized assembler for 30 battery manufacturers. HOB produces 250,000 custom battery assemblies monthly and has operations in California, Mexico, and China. HOB stocks over two million batteries and employs a large team of electrical engineers and technical salespeople, with sales representatives nationwide.

A brief article on how to choose between Lithium ION and Lithium Polymer Batteries

A Look Back

Lithium ion batteries have been commercially available since the early 1990s, possessing the highest energy density of all rechargeable battery chemistries and finding their way into almost every portable electronic device to date. In response to potential safety issues related to potential abuse events or conditions, battery pack designers and engineers have added several lines of defense with regard to battery safety. These include active circuits to maintain the battery voltage within a specific voltage window as well as short circuit protection, external PTCs to control the thermal environment of the battery pack and mechanical devices internal to the cell that disconnect the cell and arrest operation when abuse conditions occur.

In the early to mid-1990s, in response to safety considerations, as well as market pressures to make thinner and thinner cells that might not need active protection circuits, battery scientists looked for design techniques to mitigate the effects of overcharging or short circuits which could potentially harm consumers and users with shards of metal from a breeched cell can in the event of an explosion from abuse. Even though the many lines of defense were in place, continued attention to safety problems were at the forefront of engineer's minds. Lithium polymer technology provided an answer, whereby a gelled separator / electrolyte and a laminated aluminum bag substitute for a flooded electrolyte system and a sealed metal can. Less volume of volatile electrolyte was required for acceptable power rates and the bag would rupture a seal rather than violently release metal shards if over voltage or thermal runaway conditions occurred.

Polymer on the Rise

The adoption rate of lithium polymer technology in the marketplace since the early 1990s has been delayed by the instability of the supply chain as researchers struggled with manufacturing processes that combined plastics process technology with electrochemical engineering concepts, the need to manufacture the technology within reasonable economic limits and business models, and the requirement to keep pace with the rapidly growing performance of standard lithium ion chemistry. Early polymer cell and battery designs were very similar to that of conventional lithium ion batteries, offering no significant points of differentiation or enhanced product features and application engineers could not justify the tradeoffs with regard to increased design costs with the promised safety enhancements afforded by lithium polymer designs.

In the late 1990s, the combination of improving manufacturing yields, lower production costs, new and higher quality materials and a better understanding of cell design capabilities led the way to increasing the adoption rate of lithium polymer technology. Applications emerged, both in mass and niche markets, where new designs that utilized the thin, flat, form factor of lithium polymer justified design costs, market risk and consideration. Cell designs were better understood and could compete and surpass those afforded by conventional lithium ion batteries.

What's the Difference?

Lithium ion batteries consist of a cathode of lithiated metal oxide or phosphate, and a graphite anode separated by a polyethylene or polypropylene separator material in a non-aqueous electrolyte. When the battery is charged, lithium ions leave the cathode and are intercalated (inserted) into the layered structure of the graphite. As the battery discharges, lithium ions leave the anode and return to the cathode, while electrons travel in the opposite direction, completing the circuit.

Lithium polymer batteries have the same common electrochemistry as conventional lithium ion batteries - they have a lithiated oxide cathode and a graphite anode held together in a binder matrix of polyvinlydiene fluoride and coated and/or laminated to a current collector grid. However, they contain a highly porous separator, which converts to a gel when a minimum amount of electrolyte is added to operate the cell. Lithium polymer technology uses stacked plate cell architecture, as opposed to a wound "jelly roll" found in conventional lithium ion cells, which means that they consist of die-cut anode and cathode plates that are about the size of the battery and are stacked on top of each other like a deck of cards, with the plates connected in parallel.

Lithium polymer batteries have comparable energy density to lithium ion batteries and are achieving cost parity. The cells are sealed in a plastic aluminum laminate, so if the battery sees an overcharge condition, the seal ruptures and vents any gases due to electrolyte oxidation and the cell shuts down rather than having steel or aluminum casings fragment, as in the case of lithium ion batteries that may result in metal shards.

How to Choose

When our Applications Engineers receive inquiries from customers looking for small rechargeable batteries, they guide them through a number of questions in order make a sound recommendation.

First, they need to understand the application. Is it commercial, industrial, military or consumer? This invariably leads to sizing questions, mechanical constraints, and packaging parameters. From here, electrical needs are addressed including voltage, capacity and drain. And finally, yearly quantities and cost structures are discussed at very introductory levels.

From this round of discussions and guidance from the customer, a thoughtful recommendation can be made.

Generally, battery cavity restrictions and cost structures built into the product or application determine whether or not Lithium ion or Lithium polymer batteries are recommended. If an application needs a very thin battery, typically less than 4 or 5mm, lithium polymer is recommended as it can be manufactured to such degrees of thinness that can't be matched by Lithium ion. If the application's battery cavity is a bit more forgiving, then Lithium ion is typically recommended largely due it being less expensive to manufacture.

Other factors, of course, will play into whether or not Lithium ion or Lithium polymer is recommended such as weight and customization needs. But on a very general level, thickness and cost structures play a very large role in determining which battery type is right for you.

Li Ion iron phosphate's fundamental properties hold promise as an intrinsically safe cathode material for small and large platform applications.

When portable-device designers develop the latest systems with the most advanced features, much thought goes into the battery technology that powers these complex products. For over a decade, Lilon cobalt oxide has been the battery chem­istry of choice because it offers high energy density, which translates into more runtime. But more recently, thermal runaway, or battery overheating, has posed problems for users.

Today's newest Lilon technology holds the promise to make these batteries safer than ever. This technology repre­sents the pinnacle of a development process that has pro­gressed from the humble lead-acid battery through NiCd and NiMH. When compared to these older chemistries, Li­lon offers higher energy density, longer cycle life, and no memory effect.

Recently, rechargeable Lilon cells have reached an estab­lished commercial status with a production rate of several million units per month. Currently, Lilon cobalt oxide is the most commercially available variation of Lilon. Safety and thermal stability tests for lithium-manganese oxide and lithium-cobalt oxide have shown the former to be more sta­ble. And despite Lilon cobalt oxide's wide commercial acceptance, its cost, low abundance in the earth's crust, and environmental impact remain critical concerns.

New materials incorporating phosphate ions have been investigated, including Lilon iron phosphate. Due to the high availability of this chemistry compared to cobalt and manganese ions, Lilon iron phosphate is regarded as a very promising cathode material for small and large platform applications because of its enhanced thermal stability. Its low cost, non-toxicity, high abundance of iron, excellent thermal stability, safety characteristics, and good electrochemical per­formance add to an already long list of desirable criteria required for a viable cathode material.

With Lilon iron phosphate, the strong covalent bonding between the oxygen and phosphate form a strong polyanion unit that allows for greater stabilization of the staicture com­pared to layered oxides. The large polyanion also enlarges the free volume of the host's interstitial space available for lithium. The P-O-Metal bonding helps stabilize the redox energies of the metal cation and the structure, allowing a relatively fast ion migration. Consequently, oxygen atoms are harder to extract from Lilon iron phosphates.

Under normal abuse conditions, there's less likelihood of phosphate decomposition that may result in oxygen liberation from the structure. Only under extended and extensive heating (typically more than 800°C) can decomposition oc­cur in part (without oxygen release) to a Nasicon-related phase. That's important to note because it further illustrates the ability of Lilon iron phosphates to remain stable even in the harshest conditions, thus avoiding any uncontrollable thermal excursions.

Upon removal of lithium, lithiated cobalt oxide undergoes a nonlinear expansion of the unit cell. That's particularly important for battery safety because it affects the structural integrity of the material and hence its safety. Removing all the lithium available in Lilon iron phosphate causes no struc­tural modification. In fact, the structure of the fully lithiated and de-lithiated phases are similar, which confirms that the thennal stability of the Lilon iron phosphate even fully de­pleted of lithium is still better than the partially de-lithiated Lilon cobalt oxide.

With higher-energy-density batteries available, safety is of paramount concern for consumer batteries, and more advanced safety technology is required. Insight into the behavior and thermal stability of the cathode in the charged state is essential in determining the overall safety of the final cell. With that in mind, several methods are available for evaluating the safety of cells under abuse conditions. Creating an over-charge condition, for example, may lead to thermal runaway (or excessive heat), which can cause a combustion reaction in the battery because of the presence of flammable solvents and vapor mixtures in the cell. This situation would make the battery unsafe for consumer use.

Fundamental properties of Lilon iron phosphate, the material in saphion-enabled batteries, make for an intrinsi­cally safe cathode material for current Lilon applications. When fully charged, no excess lithium remains in the cath­ode (unlike Lilon cobalt oxide, where 50% still remains). This material has high resilience to oxygen loss, which would otherwise result in a significant exothermic event upon heat­ing. Polymer technology provides a system with no free elec­trolyte, unlike the commercially available liquid-based bat­teries, further adding to its safety characteristics.

M.Y. Soldi holds patents related to the phosphate cathode mate­rial in saphion iit/uum-ion technology. Valence Technology, based in Austin, TX, can be reached at. (512) 527-292J or www.valence.com.

Gerf Helles, Maxim Integrated Products

Secondary batteries can be simple devices, but improper charging can be devastating to the user experience.

The use of batteries has never been greater, particularly in light of the boom in portable devices such as mobile phones, laptops, camcorders, and MP3 players. The bat­teries are becoming smaller and lighter, even as they pack more and more energy per unit volume.

Nonrechargeable (primary) batteries create electricity from a chemical reaction that permanently transforms the cell. Discharge of the primary cell leads to a perma­nent and irreversible change in the cell chemicals. Rechargeable (secondary) batteries store rather than generate energy.

Charge or discharge current is typically expressed as a multiple of the rated capacity (C-rate). For example, a C/10 discharge current for a battery rated at 1 Ah is 1 Ah/10 =100 mA. The rated capacity of a cell is the amount of electricity it can store (produce) when fully charged under specified conditions. Thus, a battery's to­tal energy is its capacity multiplied by its voltage, result­ing in a watt-hours measurement.

Measuring performance
The cell's chemistry and design together limit the current it can source. Barring the practical factors that limit performance, a battery could produce an infinite current, if only briefly. The main impediments to infinite current are the chemicals' basic reaction rates, the cell design, and the area over which the reaction occurs. Some cells can inherently produce high currents. Short­ing a NiCd cell, for instance, produces currents high enough to melt metals and start fires.

Other batteries
The net effect of all chemical and mechanical factors in a battery can be expressed as a mathematical factor.

No battery stores energy forever. Unavoidably, the cell chemicals react and slowly degrade, causing degra­dation in the stored charge. The ratio of battery capacity to weight (or size) is the battery's storage density (see Table 1).
One question that comes to mind is, why not always choose secondary cells if primary and secondary cells ful­fill the same purpose? Secondary cells have two key drawbacks. First, secondary cells lose their electrical charge relatively quickly through self-discharge. Second,

Every charging operation applies voltage and current in a sequence that depends on the battery's chemistry. Thus, a look at chemistries reveals different requirements to be met by the charger and charging algorithm (see

NiCd cells are charged by applying a constant cur­rent ranging from 0.05C to more than 1C. Some low--cost chargers terminate the charge by means of absolute temperature. Though simple and inexpensive, this method of charge termination is not accurate. A better choice is to terminate charging when the full-charge condition is indicated by a drop in voltage. The -AV phenomenon is most useful for charging NiCd cells of 0.5C or greater. The -AV end-of-charge detection should be combined with battery-temperature measurement as well, because aging and mismatched < voltage reduce cells>

A more precise full-charge detec­tion can be achieved by sensing the rate of temperature increase (dT/dt). This charge-detection method is kinder to the battery than a fixed-temperature cutoff. Charge termination based on a combination of AT/dt and -AV cutoff enables a longer lifecy-cle by avoiding overcharge.

Fast-charging improves charge ef­ficiency. At 1C, the efficiency is close to 1.1 (91%), and the charge time for an empty pack will be slightly more than 1 hr. When apply­ing a 0.1C charge, the efficiency drops to 1.4 (71%), with a charge time of about 14 hrs.

Because a NiCd cell's charge ac­ceptance is close to 100%, almost all energy is absorbed during the initial 70% of charging, and the battery re-mains cool. Ultra-fast chargers use this phenomenon to charge a battery to the 70% level within minutes, ap­plying currents several times the C-rating without heat buildup. Above 70%, the charging continues at a lower rate until the battery is fully charged. Eventually, the battery is topped off by applying a trickle charge in the 0.02C to 0.1C range.

Table 1. Battery storage density

Charging the chemistries
Though similar to NiCd chargers, an NiMH charger employs the AT/dt method, which is the best method for charging NiMH cells. The end-of-charge voltage depression for NiMH batteries is smaller, and for small charge rates (below 0.5C, depending on temperature), there may be no voltage depression at all.

New NiMH batteries can show false peaks early in the charge cycle, causing the charger to terminate prematurely. Moreover, an end-of-charge termination by -AV detection alone al­most certainly ensures an overcharge, which in turn limits the number of possible charge/discharge cycles.

It seems there's no available < for well works that algorithm dt -dV>charging NiMH batteries under all conditions: new or old, hot or cold, and fully or partly discharged. For that reason, don't charge an NiMH battery with a NiCd charger unless it utilizes the dT/dt method for end-of-charge termination. And because NiMH cells don't absorb overcharge well, the trickle charge must be lower (about 0.05C) than that recom­mended for NiCd cells.

Slow-charging a NiMH battery is difficult, if not impossible, because the voltage and temperature profiles associated with a C-rate of 0.1C to 0.3C don't provide a sufficiently ac­curate and unambiguous indication of the full-charge state. The slow charger must therefore rely on a timer to indicate when the charge cycle should be terminated. Thus, to fully charge a NiMH battery, apply a

1. Constant-current, rapid charge of constant-voltage about 1C (or a (CCCV) charging is rate specified popular in high-end by the battery portable equipment, maker), while monitoring both voltage (AV = 0) and temperature < dt) (dT>termine when the charge should be terminated.

Whereas chargers for nickel-based batteries are current-limiting devices, chargers for Lilon batteries limit both voltage and current. The first Lilon cells called for a charge-voltage limit of 4.10 V/cell. Higher voltage means greater capacity, and cell volt­ages as high as 4-2 V have been achieved by adding chemical addi­tives. Modern Lilon cells are typi­cally charged to 4.20 V with a toler­ance of ±0.05 V/cell.

Full charge is attained after the terminal voltage reaches the voltage threshold and the charging current drops below 0.03C, which is about 3% of Icharge (see Figure 1). The time for most chargers to achieve a full charge is about 3 hrs, though some linear chargers claim to charge a Lilon cell in about an hour. Such chargers usually terminate the charge when the battery's terminal voltage reaches 4-2 V. That kind of charge determination, however, charges the battery only to 70% of its capacity.

A higher-charging current doesn't shorten the charge time by much. Higher current allows reaching the voltage peak earlier, but then the top­ping charge takes longer. As a rule of thumb, the topping charge will take twice as long as the initial charge.

Because overcharging (or overdis-charging) a Lilon cell can cause it to explode, safety is a major concern in proper charging for Lilon batteries.

The battery industry has seen significant growth due to the latest stream of portable devices. With so many hand­held products using batteries as a power source, battery manufacturers have devoted extensive R&D to make their batteries safer and lighter and with higher energy densities. That has been the predominate driver for the increase of lithium-cell chemistries at the expense of either NiCd or NiMH. A key advantage Lilon has over NiMH relates to "memory loss." Unlike the NiMH, a Lilon battery can be recharged at any point during its discharge cycle and can efficiently hold its charge, which is more than twice as long as a NiMH battery.

Another advantage of rechargeable lithium technology is its weight—it offers three times the energy density of a NiCd battery but with half the weight. Furthermore, new chip technologies combined with the latest software allow for the maximum extension of power use in the latest notebook computers, portable instruments, and cel­lular communicators.

However, care must be taken when charging a Li-lon battery in the end product, because the battery can be eas­ily damaged if the wrong voltage or current is applied. To deal with these concerns, 1C makers have designed spe­cialized charger ICs that ensure the battery is charged fully and safely under varying environmental conditions.

Squeezing a fully featured high-power charger into one 1C has always come with tradeoffs. To fit everything in a small package, most chargers included a few specialized features but at the expense of other generally desirable features.  < voltage reduce cells < for well works that algorithm dt -dV>

Nevertheless, the latest generation of chargers shares new control architectures to combine as many desirable features as possible. They support batteries up to 28 V, at charge rates up to 4 A, with efficiencies higher than 95%. Charging voltage and current accuracy are typically 0.7% and 4%, respectively. Furthermore, these pulse-width modulation (PWM) controllers, with 300- to 500-kHz synchronous architectures, can achieve 98% duty cycles, providing excellent low-dropout performance as well as continuous switching down to zero charge cur­rent. Lastly, these PWM controllers are designed to suppress the audible noise from ceramic capacitors while also allowing the use of popular inductor values for small size at high currents handling this type of storage cell. As a result, commercial Lilon packs con­tain a protection circuit that provides all electronic safety functions re­quired for applications involving rechargeable Lilon batteries: protect­ing the battery during charge, pro­tecting the circuit against excess cur­rent flow, and maximizing battery life by limiting the level of cell depletion (see Figure 2).

Protection modes

If the cell voltage sensed at vdd ex­ceeds the overvoltage threshold vqv for a period longer than the overvolt­age delay tOVD, the protection 1C should shut off the external charge FET and set an OV flag. The dis­charge path remains open during overvoltage. The charge FET is re-en­abled (unless blocked by another pro­tection condition) when the cell volt­age falls below the charge-enable threshold VCE, or discharging causes vdd"~vpls to be 8reater than vqq.

If the voltage sensed at Vj-,D drops below the undervoltage threshold Vuv for a period longer than the un­dervoltage delay tuyD, the 1C shuts off the charge and discharge FETs and sets the UV flag. When the voltage rises above Vuv and a charger is pres­ent, the 1C turns on the charge and discharge FETs.

If the cell voltage sensed at VDD drops below the depletion threshold Vsc for a period of tSCD, the 1C shuts off the charge and discharge FETs and sets the SC flag. The current path through the charge and discharge FETs isn't reestablished until the volt­age on PLS rises above VDD-VOC.
If voltage across the protection FETs (VDD-VpLS) is greater than VQC for a period longer than tQ^p, the 1C shuts off the external charge and dis­charge FETs and sets the DQC flag. The current path isn't reestablished until the voltage on PLS rises above vdd-voc-

If the 1C exceeds a predetermined temperature TMAX, the device imme­diately shuts off the external charge and discharge FETs. The FETs aren't

How much time before recharging your battery pack?

A common question when people think about battery-pack performance is: "How long until I need to recharge?" It generally doesn't matter whether it's a notebook, a data-logger, an MP3 player, a PDA, a cell phone, or a digital camcorder.

Consumers tend to compare a battery's life to a car's gas tank; how­ever, it's not that simple. The behavior of a car's driver significantly in­fluences fuel consumption. But a battery is affected by how you treat it, including the discharge rate level and frequency, how many times it has been cycled, and its environmental situation.

Today's leading semiconductor vendors offer sophisticated gas-gauge 1C algorithms that require precise analog measurement and computing capabilities as well as detailed battery characterization. Most current al­gorithms are based on measuring the cell voltages and monitoring the charge and discharge current, a technique known as coulomb counting. Looking at the cell voltage, especially with Lilon batteries, the discharge curves are relatively flat, making it difficult to determine remaining capacity.

Computing the remaining capacity based on a constant load directly correlates to the age and temperature of the battery pack throughout its life. The temperature is easily measured, but age is a different story. In simple terms, age means that the impedance and capacity have changed due to chemical reactions.

The typical capacity change after 100 cycles is about 3% to 4%, but the impedance level is nearly double. In addition, today's gas-gauge al­gorithms compensate for aging effects using certain amounts of charge and discharge to determine cycle counts. The algorithm then provides a rough estimate based on these assumptions, but the results can be un­reliable.

Under varying loads, the battery's impedance plays a bigger role. If the load increases, the voltage drop at the battery's internal resistance in­creases and switches off mechanisms to protect the battery and triggers deep discharges. Protection ICs used in Lilon packs disable further dis­charge, and the unit will stop operating, even if usable capacity remains.

Variable loads also make it hard to predict the remaining runtime. Us­ing an update for the capacity, often referred to as a "learning cycle," can help better understand usable capacity.

Current-based coulomb counting solutions enable such updates but also require certain conditions to function properly. If such a learning cy­cle doesn't occur for a period of time, or never appears, the failure rate increases up to 50% over time. With an updated system, the failure rate can be as low as 2% to 3%.

New developments are on the horizon to identify the battery's imped­ance as the main contributor to the capacity uncertainty in accounting for aging and fading. Innovative algorithms will be integrated into future gas-gauge ICs to improve how designers account for these aging effects. But the main benefactors of such battery management improvements will be the consumers turned back on until two conditions are met: Cell temper­ature drops below tmax and the host resets the OT bit.

Charging at extreme temperatures

Efforts should be made to charge at room temperature. Nickel-based batteries should only be fast-charged between 10° and 30°C. Below 5°C and above 45°C, the charge ac­ceptance of nickel-based batteries is drastically reduced.

2. Typical application Lilon cells offer reasonably good diagram for a lithium- charge performance throughout the cell protection 1C is temperature range, but below 5°C the illustrated charge rate should be less than 1C.

NiMH chargers can accommodate NiCd batteries, but not vice versa. Chargers dedicated to NiCd batteries will overcharge a NiMH battery. The cycle life and performance of nickel-based batteries are enhanced by fast-charging, because it reduces the mem­ory effect due to the formation of internal crystals. Nickel- and lithium-based batteries call for different charge algorithms. Lilon batteries need pro­tection circuitry to monitor and pro­tect against overcurrent, short circuits, overvoltage and un-dervoltage, and excessive temperature.

Gert Helles is a senior field applications engineer at Maxim's battery and thermal management group, based in Hadsten, Denmark. He holds a BSEE from the University of Southern Denmark. The company, based in Sunnyvale, CA, can be reached at (408) 737-7600 or WWW.maxim-iC.com.

BY BRION MUNSEY
House of Batteries
Huntington Beach, CA

Although the battery is the lifeblood of today's portable electronic devices, it is amazing how often this critical component has been left out by engineers until the last minute in the design process. Because battery technology has not evolved at the rapid rate that semiconductors or some other electronic components have over the last 20 years, the battery can be one of the more limiting factors in an electronic design.

There are more batteries to choose from now than ever, and each type of battery chemistry offers distinct advantages and disadvantages. A number of critical questions need to be addressed when selecting a battery for a new application.

It is important to review every detail of a battery's specification before implementing it into your new design.

Cost
Low cost is often thought of as the primary factor when selecting a battery type. We would all like to see a battery the size of a pinhead with thousands of ampere-hours of capacity that costs only pennies.

The reality is, however, that on many occasions a higher initial battery cost pays for itself in long-term benefits. Cost vs. specific performance needs should be addressed early in the design process. Set a reasonable target price, but expect it to move up or down based on your specific needs.

Primary or secondary usage
Primary cells are "one-time-use" batteries. Once the chemical reaction takes place, the cell loses its ability to produce energy; it is then discarded and replaced with a fresh cell or battery. Applications that see infrequent use or long-term use at very low drain rates are good candidates for primary cells.

Secondary batteries are "rechargeable," and the chemical reaction that takes place within the cell is reversible and repeatable for perhaps thousands of times depending on the chemistry and application. Any application that sees a lot of daily use, such as cellular phones and laptop computers, are good choices for rechargeable batteries.

Voltage
Most cells operate over a specific voltage range. For example, an alkaline cell has a nominal voltage of 1.5 V, an open-circuit voltage of 1.6 V if it is fresh, and is not completely discharged until it reaches 0.8 V or less under load.

NiCd cells have a nominal voltage of 1.2 V, an open-circuit voltage of 1.3 V or more for a freshly charged cell, and are not completely discharged until they reach 0.8 V or less under load. Multiply the number of cells in series, and you can have a fairly broad voltage range that your circuit has to deal with.

Discharge current
If the discharge current is intermittent, determine the amplitude and duration of minimum and peak current drains. Most electronic devices use varying amounts of current as they are used. A cellular phone is probably the best example: During transmission a cell phone can consume 1 to 2 A in short pulses, while its standby current is something like 100 mA or less.

Some batteries might do well at the lower drain rate, but fail to perform under peak current demand. Be sure to select a cell that can maintain a high voltage relative to the nominal voltage under peak loads.

Drain rate
How fast will your battery be used up? Will the load be a few microamperes, or will it be 10 to 50 A or more?

Lithium coin cells do well at low loads over long periods. Alkaline cells perform better under more demanding loads than carbon zinc or zinc chloride and even most lithium cells.

In rechargeables, lead-acid and NiCd are good choices for high-rate applications. Newer NiMH cells will perform well at higher drain rates also.

A battery may be discharged under different modes depending on the equipment load. The type of discharge mode selected will have a significant impact on the service life delivered by a battery in a specified application. Three typical modes under which a battery may be discharged are the following:

Constant resistance (R): The resistance of the equipment load remains constant throughout the discharge.

Constant current (C): The current drawn by the device remains constant during the discharge.

Constant power (P): The current during the discharge increases as the battery voltage decreases, thus discharging the battery at a constant power level (Power = Current x Voltage).

Operation
Will the application be used often or will it sit in storage most of the time? For example, a flashlight used only on an occasional camping trip is probably better suited to a nonrechargeable alkaline battery, which stores well and has plenty of power.

A flashlight that's used everyday would be better off with some kind of rechargeable battery, because the cost of constantly replacing primary batteries would become prohibitive. Some rechargeable chemistries like NiCd and NiMH are better suited to continuous discharges, while lead-acid batteries perform better in standby applications such as uninterruptible power supplies.

Temperature
An often-overlooked aspect of battery performance, temperature is nevertheless a major consideration when selecting a battery. Batteries do not charge or discharge well at low temperatures.

High temperatures are detrimental to shelf life (self-discharge). Most batteries perform best in the –20° to +60°C range. Lithium primary cells do better than most chemistries at both temperature extremes. Some lead-acid batteries do well at –40°C, and special "high-temperature" NiCds are designed to perform at +70°C.

Size
The semiconductor revolution has led to a dramatic reduction in the size of portable electronic devices over the last decade. Batteries are often the largest single component of a portable electric device.

Batteries have lagged behind silicon in terms of size reduction. Lithium coin, silver oxide, and zinc air batteries are all small primary cells that work well in pocket-sized devices.

In rechargeables, significant improvements have been made in both NiCd and NiMH chemistries giving them much higher ampere-hour ratings than they had just 10 years ago. Further reductions in size and particularly weight have been achieved with Li-ion and lithium-polymer chemistries.

Weight
The recent evolution of electronic devices is also consistently driving their weight down. Batteries are also often the heaviest component in a portable electronic device.

Carbon-based primary batteries are lighter than alkaline, but with less performance and shelf life. Lithium cells are lighter than other primary chemistries and have superior shelf life and performance. Li-ion and lithium-polymer chemistries are far lighter than other rechargeable batteries the same size and have improved the portability of many electronic devices.

Charge rate
If your battery is a secondary type, how fast do you need to recharge it? On average, 140% of the energy taken out of a rechargeable cell needs to be replaced when recharging it.

Lead-acid batteries (at a C/300 charge rate) and some special NiCds (at a C/20 to C/30 charge rate) do well on continuous-float or trickle charges for "standby" applications. A 14-hour charge (at a C/10 charge rate) is considered "standard" for sealed lead-acid, NiCd, and NiMH batteries.

Seven-hour fast charges are possible for most secondary chemistries. If you require a rapid charge of 1 hour or less then NiCd and some NiMH cells are a good choice. Li-ion and lithium-polymer batteries require a special two-stage charge that usually takes 3 hours to complete.

Storage requirements
How much shelf life do you need? A battery is said to be "spent" when it cannot deliver at least 80% of its rated capacity. How quickly will a cell lose its energy just sitting on the shelf?

Most primary batteries will store well for several years at room temperature. Carbon-based primary cells last about two years on the shelf, alkalines five years, and lithium cells 10 years or more.

Rechargeable or secondary batteries lose their charge when put into storage after charging. Lead-acid batteries need a "top charge" about every 6 months. NiCds last about 90 days to 80% capacity, NiMH cells lose their charge in four weeks, and lithium rechargeables can sit for perhaps several months at room temperature. Higher ambient temperatures during storage will reduce the shelf life of all batteries, perhaps significantly.

Cycle life
If your battery is rechargeable, how many recharges do you need? Lead-acid batteries will deliver from 200 to thousands of cycles depending on how deep each discharge cycle is.

NiCds will deliver from 500 to thousands of cycles, depending on how they are used. NiMH cells are good for several hundred cycles or more. Li-ion and lithium polymer will yield several hundred cycles.

Rechargeable batteries are sensitive to the recharge regime given to them. In other words, the better--and generally more expensive--the charger is, the better the long-term performance of the battery.

Recycling
Currently, by law all rechargeable chemistries must be recycled. This includes sealed lead-acid, NiCd, NiMH, and even Li-ion. These batteries must be clearly marked with the "chasing arrows" symbol and a national toll-free phone number that end users may use to locate their local recycling center.
When rechargeable batteries are purchased, a fee covers the cost of recycling. These fees may be invoiced as a separate line item, or they may be added to the overall battery price. Either way, they must be paid.

It is important to review every detail of your battery's specification before you implement it into your new design. That way you will be able to predict the battery's performance with some accuracy. Of course, after selection, careful testing is needed in the application to ensure that no unexpected behaviors prevent your new design from performing at its best.

What do TV remote controls, cordless tools and flashlights have in common?
They are all battery-powered devices. Believe it or not, there is a lot to learn about batteries, such as proper use, storage, disposal and the differences between battery types – Alkaline, Lithium and Nickel Metal Hydride or NiMH.

Batteries 101

• Read the instructions on your battery-operated device before installing the batteries. Insert the batteries properly, following the symbols that show the correct placement for positive (+) and negative (-) ends.
• Never recharge a battery unless it is specifically marked “rechargeable.” Attempting to recharge an alkaline or other non-rechargeable battery could result in rupture or leakage.
• Do not use rechargeable alkaline batteries in a nickel cadmium or nickel-metal-hydride battery charger.
• Keep battery contact surfaces clean by gently rubbing with a clean pencil eraser or cloth.
• Always keep batteries away from children.
• Replace batteries with the size and type specified by the manufacturer.
• Remove all used batteries from your equipment at the same time, replacing with all new batteries of the correct size and type. Mixing old and new batteries or different types and makes of batteries could cause rupture or leakage.

Extending Battery Life

• Store batteries in a dry place at normal room temperature. Always keep batteries or battery-powered equipment away from heat.
• Remove batteries from devices to be stored for extended periods.
• Handle batteries with care – never carry loose batteries in a pocket or purse with metal objects such as coins or paper clips. This can short-circuit the battery and generate excessive heat.
• Never dispose of batteries in fire – rapid temperature increase may cause the battery to explode.

Recycling – Doing your part for the environment
All independent studies show batteries to be environmentally unimportant when disposed of as normal household waste. As battery users, consumers have a hand in protecting the environment by using batteries wisely to ensure full service life. Keep these helpful tips in mind:

• Turn off battery-operated devices when not in use to prevent waste of battery life.
• Batteries can self-discharge even when power is not supplied to the device. Don't leave batteries in devices being stored.
• Batteries should be stored in original packaging without the contacts touching.
• Avoid temperature extremes such as refrigerators or attics – cold and heat can reduce battery shelf life.
• Mixing old and new batteries forces the older battery to keep working even after its life has been exhausted. This can lead to additional internal gases being produced within the old battery and can result in leakage or rupture.
• Do not open battery casings. Batteries contain materials that may cause personal harm.
• Car batteries that contain lead should be disposed of only at waste management recycling centers. Local auto retailers or service centers may also purchase used car batteries for recycling.
• Nickel-cadmium or lead-acid type rechargeable batteries contain heavy metals and should be recycled. Check with your local government recycling coordinators for the nearest recycling center or call 1-800-8BATTERY.