Let Us Learn Why Do Some Batteries Last Longer Than Others

It's Monday and you're late for work thanks to the sudden death of your alarm clock's batteries--the same ones you replaced not too long ago. Yet while they only lasted a few weeks, the hp batteries in your remote control have thrived for over a year. So what's the difference between them? Is it the brand? Do more expensive batteries really last longer? And why do some batteries, even when they're the same brand, last longer than others?

When you insert batteries into a device, they have to be positioned in the battery compartment with the positive and negative sides, or terminals, facing a certain way. When properly inserted, the terminals then line up with a wire spring inside the device. This wire acts as a bridge between the two terminals, allowing electrons to flow from the hp pavilion dv8000 battery into the wire, thereby charging the device and enabling it to function.

Batteries have a very long shelf life, typically lasting a year or more without losing power. Chances are, if a store is selling it, it has not yet expired and will work the same regardless of whether it's purchased a day or a year before its expiration date. So you really shouldn't have to be too concerned with the age of a hp 484784-001 battery and don't need to look for the pack with the latest expiration date stamped on it. However, even if they aren't ever activated, batteries can lose up to 20 percent of their original power per year if they're kept in a warm area (about 68 to 86 degrees F). Known as the battery's self discharge rate, this loss of power can be reduced if batteries are stored at lower temperatures. On the same token, however, extremely low temperatures can also reduce a hp compaq nc6000 battery's charge. So while it may help to store your batteries in a refrigerator, the freezer isn't such a great idea.

Assuming you already store your batteries at an appropriate temperature, what else determines whether or not they last a week, a month or a year? Well, contrary to what those commercials may state, it's really more about the type of the hp compaq 6910p battery rather than the brand. An AAA battery, for example, will last longer than a D battery. In addition, a battery's life is greatly influenced by the product in which it is used and the amount of energy required to make the device work. Although most products like CD players and clocks tend to use less energy, others such as MP3 players and cameras typically require more energy. Lithium, titanium and premium alkaline batteries are designed for these high-energy devices, whereas regular alkaline batteries work best with low-energy devices. In terms of brands, countless studies have been done with independent testing from companies like TechTV and Zbattery.com, but there has been no conclusive proof that any particular brand works better than any other. Rather, the factors that determine how long hp compaq 6710b battery is based on how they're stored and how they're used.

Heat, Loading and Battery Life

Heat is a killer of all batteries and high temperatures cannot always be avoided. This is the case with a apple computerbattery inside a laptop, a starter battery under the hood of a car and stationary batteries in a tin shelter under the hot sun. As a guideline, each 8°C (15°F) rise in temperature cuts the life of a sealed lead acid battery in half. A VRLA batteryfor stationary applications that would last 10 years at 25°C (77°F) would only live for five years if operated at 33°C (95°F). Once the battery is damaged by heat, the capacity cannot be restored. The life of a battery also depends on the activity and is shortened if the battery is stressed with frequent discharge.

According to the 2010 BCI Failure Mode Study, starter batteries have become more heat-resistant over the past 10 years. In the 2000 study, a change of 7°C (12°F) affected battery life by roughly one year; in 2010 the heat tolerance has widened to 12°C (22°F). In 1962, a starter battery lasted 34 months, and in 2000 the life expectancy had increased to 41 months. In 2010, BCI reports an average age of 55 months of use. The cooler North attains 59 months and the warmer South 47 months.

Cranking the engine poses minimal stress on a starter apple a1175 battery. This changes in a start-stop function of a micro hybrid. The micro hybrid turns the IC engine off at a red traffic light and restarts it when the traffic flows. This results in about 2,000 micro cycles per year. Data obtained from car manufacturers show a capacity drop to about 60 percent after two years of use in this configuration. To solve the problem, automakers are using specialty AGM and other variations that are more robust than the regular lead acid. Read more about Alternate Battery Systems. Figure 5 shows the drop in capacity after 700 micro cycles. The simulated start-stop test was performed in Cadex laboratories. CCA remains high.

Figure 5: Capacity drop of a flooded starter battery when micro cycling Start-stop function on a micro hybrid stresses the battery; the capacity drops to about 50 percent after two years of use. AGM is more robust for this application. Courtesy of Cadex, 2010

Test method:   The test battery was fully charged and then discharged to 70 percent to resemble the SoC of a micro hybrid in real life. The battery was then discharged at 25A for 40 seconds to simulate engine off condition at stoplight with the headlight on, before cranking the engine at 400A and recharging. The CCA readings were taken with the Spectro CA-12.

The cell voltages on a apple a1185 battery string must be similar, and this is especially important for higher-voltage VRLA batteries. With time, individual cells fall out of line, and applying an equalizing charge every six months or so should theoretically bring the cells back to similar voltage levels. While equalizing will boost the needy cells, the healthy cell get stressed if the equalizing charge is applied carelessly. What makes this service so difficult is the inability to accurately measure the condition of each cell and provide the right dose of remedy. Gel and AGM batteries have lower overcharge acceptance than the flooded version and different equalizing conditions apply. Always refer to the manufacturer’s specifications.

Water permeation, or loss of electrolyte, is a concern with sealed lead acid batteries, and overcharging contributes to this condition. While flooded systems accept water, a fill-up is not possible with VRLA. Adding water has been tried, but this does not offer a reliable fix. Experimenting with watering turns the VRLA into unreliable battery that needs high maintenance.

Flooded lead acid batteries are one of the most reliable systems. With good maintenance these batteries last up to 20 years. The disadvantages are the need for watering and providing good ventilation. When VRLA was introduced in the 1980s, manufacturers claimed similar life expectancy to flooded systems, and the telecom industry switched to these maintenance-free batteries. By mid 1990 it became apparent that the life for VRLA did not replicate that of a flooded type; the useful service life was limited to only 5–10 years. It was furthermore noticed that exposing the batteries to temperatures above 40°C (104°F) could cause a thermal runaway condition due to dry-out.

A new lead acid battery should have an open circuit voltage of 2.125V/cell. At this time, the apple powerbook g4 12 battery is fully charged. During buyer acceptance, the lead acid may drop to between 2.120V and 2.125V/cell. Shipping, dealer storage and installation will decrease the voltage further but the battery should never go much below 2.10V/cell. This would cause sulfation. Battery type, applying a charge or discharge within 24 hours before taking a voltage measurement, as well as temperature will affect the voltage reading. A lower temperature raises the OCV; warm ambient lowers it. 

Battery Definitions

Batteries come in all shapes and sizes and there could be as many types as there are species of dog. Rather than giving batteries unique names as we do with pets, we distinguish batteries by chemistry, voltage, size, specific energy (capacity), specific power, (delivery of power) and more. A battery can operate as a single cell to power a cellular phone, or be connected in series to deliver several hundred volts to serve a UPS (uninterruptible power supply system) and the electric powertrain of a vehicle. Some batteries have high capacity but cannot deliver much power, while a starter battery has a relatively low capacity but can crank the engine with 300A.

The largest battery systems are used for grid storage to store and delivery energy derived from renewable power sources such as wind turbines and solar systems. A 30-megawatt (MW) wind farm uses a storage battery of about 15MW. This is the equivalent of 20,000 starter batteries and costs about $10 million. One mega-watt feeds 50 houses or a super Walmart store. Let’s now examine each of the hp pavilion dv6 battery characteristics further.

Chemistry
The most common chemistries are lead, nickel and lithium. Each system requires its own charging algorithm. Unless provisions are made to change the charge setting, different battery chemistries cannot be interchanged in the same charger. Also observe the chemistry when shipping and disposing of batteries; each type has a different regulatory requirement.

Voltage
Voltage describes the nominal open circuit voltage (OCV), which varies with chemistry and number of cells connected in series. Always observe the correct voltage when connecting to a load or a charger. Do not proceed if the voltage does not agree.

Capacity
Capacity represents the specific energy in ampere-hours (Ah). Manufacturers often overrate a hp pavilion dv7 battery by giving a higher Ah rating than it can provide. You can use a battery with different Ah (but correct voltage), provided the rating is high enough. Chargers have some tolerance to batteries with different Ah ratings. A larger battery will take longer to charge than a small one.

Cold cranking amps (CCA)
CCA specifies the ability to draw high load current at –18°C (0°F) on starter batteries. Different norms specify dissimilar load durations and end voltages.

Specific energy and energy density
Specific energy orgravimetric energy density defines the battery capacity in weight (Wh/kg); energy density or volumetric energy density is given in size (Wh/l). A battery can have a high specific energy but poor specific power (load capability), as is the case in an alkaline battery. Alternatively, a battery may have a low specific energy but can deliver high specific power, as is possible with the supercapacitor. Specific energy is synonymous with battery capacity and runtime.

Specific power
Specific power or gravimetric power density indicates the loading capability, or the amount of current the hp pavilion dv8 battery can provide. Batteries for power tools exhibit high specific power but have reduced specific energy (capacity). Specific power is synonymous with low internal resistance and the delivery of power.

C-rates
C-rates specify charge and discharge currents. At 1C, the battery charges and discharges at a current that is par with the marked Ah rating; at 0.5C the current is half, and at 0.1C it is one tenth. On charge, 1C charges a good battery in about one hour; 0.5C takes 2 hours and 0.1C 10 to 14 hours. Read more about What is the C-rate?

Load
Also known as electromotive force (EMF), the load draws energy from the battery. Internal hp battery resistance and depleting state-of-charge cause the voltage to drop.

Watts and Volt-amps (VA)
Power drawn from a battery is expressed in watts (W) or volt-amps (VA). Watt is the real power that is being metered; VA is the apparent power that determines the wiring sizing and the circuit breakers. On a purely resistive load, watt and VA readings are alike; a reactive load such as an inductive motor or florescent light causes a drop in the power factor (pf) from the ideal one (1) to 0.7 or lower. For example, a pf of 0.7 has a power efficiency of 70.

The Cost of Portable Power

Electrical energy from non-rechargeable  batteries is expensive in relative terms and its use is limited to low power applications such as watches, flashlights and portable entertainment devices. Cell phones, laptops and power tools run mainly on rechargeable (secondary) batteries.

In this paper we calculate the cost to produce 1000 watts of power for one hour (1kWh) from different energy storage medias. We first look at primary and secondary batteries; then compare the energy cost derived from an internal combustion motor, the fuel cell and finally the electrical grid.

The primary battery

Figure 1 reveals the cost of energy using commercial alkaline cells. The right column shows a lithium battery for still cameras and memory backup.

It can be seen that larger cells provide a lower cost per kWh than small cells. The energy cost from the AA is more than half that of the smaller AAA. The C cell provides the lowest cost per kWh. The D cell has gone up in cost because of moderate use. Advanced systems, such as lithium, provide very high energy density at a premium cost. The energy cost of the 6-volt camera battery is more than ten times that of an alkaline C cell.

Figure 1: Cost of energy obtained by primary batteries. The energy cost from primary batteries is high and increases with smaller battery sizes and systems with high energy densities. _______________ *The nominal voltage is used to calculate the Wh. Because of falling voltage during discharge, the actual energy is less than what is shown.

Primary batteries hold more energy than secondary batteries per size and weight. Operational readiness, long storage and instant readiness are other benefits. Primary batteries contain little toxic substances and are considered environmentally friendly.

The secondary battery

Secondary batteries provide far more economical energy than primaries, as Figure 2 reveals. This analysis is based on the estimated purchase price of a commercial battery pack and on the number of discharge-charge cycles it can endure before replacement is necessary. The calculated cost does not include the electricity needed for charging, nor does it account for the purchasing cost of the charging equipment.

Figure 2: Energy and cost comparison using rechargeable cells. Older chemistries are generally cheaper in costs per kWh than newer systems. Larger batteries are more cost-effective than smaller ones.

Newer chemistries provide higher energy densities than conventional batteries per size and weight but the cost per kWh is higher. This cost is, to a large extent, governed by the number of charge/discharge cycles the battery can endure.

The low costs of nickel-cadmium can only be achieved by applying a full discharge once every 1-2 month as part of a maintenance program to prevent memory. If omitted, nickel-cadmium is on par with nickel-metal-hydride and lithium-ion in terms of cycle life. Lack of maintenance would increase the cost three-fold. Environmental conditions, such as elevated temperatures and incorrect charging, reduce the expected sony battery life of all battery chemistries. The calculated cycle life is based on best cases.

By far the lowest cost per kWh is lead-acid for wheelchairs and scooters. Running a laptop off a large lead-acid battery would reduce the energy cost twenty fold. This, however, would be a hard sell. 

The combustion engine 

Figure 3 compares the energy cost to generate 1kW of energy from the primary AA alkaline cells, a nickel-cadmium pack, a combustion engine used in a midsize car, fuel cells and the electrical grid. The cost estimation takes into account the initial investment, fuel costs where applicable and eventual replacement of the systems.

Figure 3: Cost of generating 1kW of energy. This takes into account the initial investment, fuel consumption where applicable, maintenance and eventual replacement of the equipment. The lowest cost power source is the utility; the most expensive is primary batteries

The fuel cell

The fuel cell offers the most effective means of generating electricity but is expensive in terms of cost per kWh. Fuel cells, as a fujitsu battery replacement, will only become economically viable once such units are available in compact design at a reasonable price.

Fuel cells for stationary applications are still more expensive than diesel. The least viable application in terms of cost is fuel cells for vehicles. The internal combustion motor, as we know it today, is hard to beat. According to the US Department of Energy, hydrogen is four times as expensive as gasoline and the fuel cell is ten times as expensive to build as a gasoline engine. Incentives other than cost may be needed to entice motorists to switch to the environmentally friendly fuel cell.

The lowest cost per kWh is electricity from the grid. The energy can be generated in remote locations. The transportation maintenance and costs are relatively low. All costing information is based on current estimates and assumptions.

How does Internal Resistance affect Performance?

With the move from analog to digital, new demands are placed on the battery. Unlike analog portable devices that draw a steady current, the digital equipment loads the battery with short, heavy current spikes.

One of the urgent requirements of a battery for digital applications is low internal resistance. Measured in milliohms, the internal resistance is the gatekeeper that, to a large extent, determines the runtime. The lower the resistance, the less restriction the battery encounters in delivering the needed power spikes. A high mW reading can trigger an early 'low battery' indication on a seemingly good battery because the available energy cannot be delivered in the required manner and remains in the battery

Figure 1 demonstrates the voltage signature and corresponding runtime of a battery with low, medium and high internal resistance when connected to a digital load. Similar to a soft ball that easily deforms when squeezed, the voltage of a battery with high internal resistance modulates the supply voltage and leaves dips, reflecting the load pulses. These pulses push the voltage towards the end-of-discharge line, resulting in a premature cut-off. As seen in the chart, the internal resistance governs much of the runtime.

Figure 1: Discharge curve on a pulsed load with diverse internal resistance. This chart demonstrates the runtime of 3 batteries with same capacities but different internal resistance levels.

Talk-time as a function of internal resistance 

As part of ongoing research to measure the runtime of batteries with various internal resistance levels, Cadex Electronics examined several cell phone batteries that had been in service for a while. All batteries were similar in size and generated good capacity readings when checked with a battery analyzer under a steady discharge load. The nickel-cadmium pack produced a capacity of 113%, nickel-metal-hydride checked in at 107% and the lithium-ion provided 94%. The internal resistance varied widely and measured a low 155 mOhm for nickel-cadmium, a high 778 mOhm for nickel-metal-hydride and a moderate 320 mOhm for lithium-ion. These internal resistance readings are typical of aging batteries with these chemistries.

Let's now check how the test batteries perform on a cell phone. The maximum pulse current of a GSM (Global System for Mobile Communications) cell phones is 2.5 amperes. This represents a large current from a relatively small battery of about 800 milliampere (mAh) hours. A current pulse of 2.4 amperes from an 800 mAh battery, for example, correspond to a C-rate of 3C. This is three times the current rating of the battery. Such high current pulses can only be delivered if the internal battery resistance is low.

Figures 2, 3 and 4 reveal the talk time of the three lithium-ion batteries under a simulated GSM current of 1C, 2C and 3C. One can see a direct relationship between the battery's internal resistance and the talk time. nickel-cadmium performed best under the circumstances and provided a talk time of 120 minutes at a 3C discharge (orange line). nickel-metal-hydride performed only at 1C (blue line) and failed at 3C. lithium-ion allowed a moderate 50 minutes talk time at 3C.

Figure 2: Discharge and resulting talk-time of nickel-cadmium at 1C, 2C and 3C under the GSM load schedule. The battery tested has a capacity of 113%, the internal resistance is a low 155 mOhm.

Figure 3: Discharge and resulting talk-time of nickel-metal-hydride at 1C, 2C and 3C under the GSM load schedule. The battery tested has a capacity of 107%, the internal resistance is a high 778 mOhm.
Figure 4: Discharge and resulting talk-time of a lithium-ion battery at 1C, 2C and 3C under the GSM load schedule. The battery tested has a capacity of 94%, the internal resistance is 320 mOhm. 

Internal resistance as a function of state-of-charge

The internal resistance varies with the state-of-charge of the toshiba satellite a350 battery. The largest changes are noticeable on nickel-based batteries. In Figure 5, we observe the internal resistance of nickel-metal-hydride when empty, during charge, at full charge and after a 4-hour rest period.

The resistance levels are highest at low state-of-charge and immediately after charging. Contrary to popular belief, the best battery performance is not achieved immediately after a full charge but following a rest period of a few hours. During discharge, the internal battery resistance decreases, reaches the lowest point at half charge and starts creeping up again (dotted line).

Figure 5: Internal resistance in nickel-metal-hydride. Note the higher readings immediately after a full discharge and full charge. Resting a battery before use produces the best results. References: Shukla et al. 1998. Rodrigues et al. 1999.

The internal resistance of lithium-ion is fairly flat from empty to full charge. The battery decreases asymptotically from 270 mW at 0% to 250 mW at 70% state-of-charge. The largest changes occur between 0% and 30% SoC.

The resistance of lead acid goes up with discharge. This change is caused by the decrease of the specific gravity, a depletion of the electrolyte as it becomes more watery. The resistance increase is almost linear with the decrease of the specific gravity. A rest of a few hours will partially restore the battery as the sulphate ions can replenish themselves. The resistance change between full charge and discharge is about 40%. Cold temperature increases the internal resistance on all batteries and adds about 50% between +30°C and -18°C to lead acid batteries. Figure 6 reveals the increase of the internal resistance of a gelled lead acid toshiba satellite a200 battery used for wheelchairs. 

Figure 6: Typical internal resistance readings of a lead acid wheelchair battery. The battery was discharged from full charge to 10.50V. The readings were taken at open circuit voltage (OCV). Cadex battery laboratories.

Batteries for Transportation, Aerospace

Battery-powered Vehicles

Batteries for propulsion systems have been in use for over 100 years, and today electric powertrains drive robots, bicycles, wheelchairs, golf cars, forklifts, EVs and underwater vessels. This power source has one thing in common; it is pollution-free and can be used indoors and underwater. For reasons of battery size, propulsion systems for heavy outdoor equipment such as earthmoving machines, non-electrified trains, aircraft and large ships must continue to rely on fossil fuel.

Most electric bicycles in developing countries run on lead acid batteries. While inexpensive, lead acid for deep-cycle use is ill suited and the batteries last for only 9 to 12 months on a daily commute. Nickel- or lithium-based batteries with twice and three-times the specific energy offer better cycle performance and shorter charge times but are expensive. While lead acid comes in at less than $100 a pack, a nickel-based battery costs $400–500, and a high-end Li-ion goes for $800–1,200. At a capacity of 280–480Wh, the battery has a range of 20–40km. With flat terrain and good wind conditions, the battery power with 70 percent pedal assist is only 1kW per kilometer (1.6kW per mile). Uphill propulsion consumes up to 10Wh/km (16kW per mile).

The battery cost dictates the developing world to choose lead acid. If the commuter had a bit more money he would likely buy a motorcycle. In the wealthy West, bicycle owners use their bicycles more as a form of recreation than a necessity. They have the means to go for a better battery, and advanced e-bikes with NiMH and Li-ion batteries sell for several thousand dollars. Europe is leading in the up-scale electrical bicycle and the trend is spreading.

Wheelchairs, scooters and golf cars use mostly lead acid batteries. Even though heavy, lead acid works reasonably well and alternative chemistries would be too expensive. While wheelchair batteries tend to have a short service life span of about two years, a similar battery in a golf car can last for 4 to 5 years. This, I believe, is due to charging practices. The lead acid battery needs a fully saturated charge of 14–16 hours to prevent sulfation, and the time is not always available for the daily wheelchair user who may only charge the battery for eight hours while asleep. Golf car batteries, on the other hand, typically receive the needed 14–16 hours in a full overnight charge.

Ever since the starter motor was invented in 1912, lead acid batteries began cranking engines and providing power for lighting and ignition. Low cost and high current loading make lead acid an almost perfect candidate for starter applications. A typical starter battery has about 720 watts, and one of its unique qualities is good cranking ability even when the capacity fades to 25 percent or less.
Hybrids, plug-ins and electric vehicles use larger batteries, and Figure 1 compares the battery sizes. While the hybrid can get by with a battery twice the size of a starter battery, plug-in vehicles carry batteries in the 5–15kWh range, and the pure EV includes a monster battery ranging from 20 to 50kWh. Read more about the Electric Vehicle.




Figure 1: Typical battery wattages of vehicle batteries. While starter and hybrid batteries are tolerant to capacity fade, a weak EV battery travels shorter distances.
Courtesy of Cadex

The automotive industry is very conservative, and the choice of toshiba pa3819u-1brs battery for most modern electric powertrains is lithium-ion with a nickel-manganese-cobalt mix (NMC). These cells provide stable service for many years and have low self-discharge, even when aging. NMC is also a desirable battery for power tools. Another strong candidate is Li-phosphate, a battery that delivers the best cycle life and is safe but has higher self-discharge than NMC. This complicates battery management, especially if the cells age differently.

University students converting an old Volkswagen Beetle to an electric powertrain to drive around the globe would shop for a lower-priced alternative and likely find a source in China. China offers Li-ion mono-blocks in 40–800Ah sizes at attractive prices. These batteries work well for less demanding applications and are great for experimental uses. There is, however, concern about safety and reliability when placed into the hands of common consumers.

The need of a battery management system becomes evident. It prevents any cell from exceeding 4.25V/cell on charge and dropping below 3.00V on discharge. As the cells age, cell capacities diverge and this affects charge and discharge times. On charge, a weak cell reaches full charge first, and without limit the voltage would rise further. On discharge, the weak cell discharges first and needs protection from voltage depletion. Weak cells are at a disadvantage; they get stressed the most and lose capacity quicker than the strong cells in a pack.

Forklifts use mostly lead acid batteries. Here, the weight is of little concern, however, long charging times is a disadvantage for warehouses operating 24 hours a day. This limits the fleet operation to only one shift. Fuel cell makers are gaining inroads by offering charging while the vehicle is in use. The addition of a fuel cell serving as onboard charger reduces battery size, but eliminating the battery entirely is not possible. The fuel cell has poor response characteristics on power demand and lacks the needed power bandwidth; the toshiba pa3450u-1brs battery fills in for these shortcomings. Read more about the fuel cell.

The heavier the wheeled application, the more difficult it becomes to use batteries as the main powertrain. This does not prevent engineers from looking into alternate power sources to replace polluting diesel engines. One application under consideration is to use batteries for the Automatic Guided Vehicle (AGV) systems at ship ports, but battery size and charging times make this unfeasible. AGVs run 24 hours a day and the vehicles cannot be removed for lengthy charging. An automated battery exchange is being considered by removing the 10-ton, 300kWh lead acid battery from the vehicle and putting it on charge. Cost and impracticality may limit such an approach.

A German firm looked at using lithium-ion batteries for AGVs to speed up charging and reduce weight. While many smaller applications have switched to this new battery system, Li-ion is not yet ready for very large applications; the cost is prohibitive and the safety of such systems remains in issue.

On large-scale applications, batteries continue to have a hard time competing with fossil fuel in terms of specific energy. While a modern Li-ion battery produces about 120Wh/kg of energy, the net calorific value (NCV) of fossil fuel is 12,000Wh/kg, or one liter, an energy that is one hundred times higher. Even at a low efficiency of 25 percent, which an IC engine delivers, batteries don’t come close to this delivery of power.

Will Li-ion advance to take this spot? Perhaps not in our lifetime. Even if modern technology enabled large energy storage devices, charging these mega-batteries in an hour could dim a city. Replacing large diesel engines with batteries does not make commercial sense for now, nor can the fuel cell fill the spot. We need to breathe diesel-polluted air a little longer.

Batteries for Aviation

The duty of batteries on board aircraft is to run navigation and emergency systems when the Auxiliary Power Unit (APU) is off or if an emergency occurs. In the event of an engine failure, the batteries must supply energy from 30 minutes to three hours. Each aircraft must also have enough toshiba pa3594u-1brs battery power to facilitate a safe landing.

Starting a large aircraft involves two stages. Most commercial jet aircraft use flooded nickel-cadmium to first engage the APU located at the tail end of a plane. The APU takes significantly longer to start and requires more energy than cranking the reciprocating engine in a vehicle. The spooling speed of the APU must be sufficiently high to attain compression for self-sustained ignition. This takes about 15 seconds and consumes 15kW of energy. Once running, an air compressor or hydraulic pump jumpstarts the large jet engines. On smaller aircraft, the battery must spool each engine for 25–40 seconds at high current. This puts far more stress on a battery than starting a car, and the batteries must be built accordingly.

Smaller aircraft may use a sealed lead-tin battery that is heavier than NiCd but has lower maintenance. The 12 and 24V aviation batteries are rated in IPP and IPR rather than CCA, as is common in the auto industry. Modern jet fighters spool the engines with lithium-ion batteries.

Durability and good performance at low temperature are the main reasons for the continued use of nickel-cadmium batteries in aviation. Most are flooded and require high maintenance that includes exercising to eliminate memory. The service consists of totally discharging the battery and placing a shortening strap across each cell for 24 hours. Each toshiba satellite a200 battery is also checked for capacity with a battery analyzer.

Although aircraft carry many batteries aboard, their sole purpose is to provide starting and backup power. No passenger would dare fly to Europe or Asia on battery power alone. One can clearly see the limitations of batteries for large engines, and we need to rely on fossil fuel a little bit longer. (Let’s not give away this precious nonrenewable resource too cheaply by allowing people to squander the oil, especially if alternative energy storage devices, i.e. the batteries, can be used for ground transportation.)

Batteries for Aerospace

Early satellites used exclusively NiCd batteries. This, by the way, exposed the “memory” phenomenon in that NiCd could remember the amount of energy that was used on a tightly regulated discharge schedule. If the discharge lasted longer than normal, the battery would suffer a mysterious voltage drop. Today, most modern satellites, including the Hubble, use nickel-hydrogen cells. One of the enduring qualities of nickel-hydrogen is long cycle life. To optimize longevity, engineers over-design the batteries to achieve a small depth of discharge of only 6 to 10 percent.

High price and large size limit nickel-hydrogen batteries for satellite applications. Each cell has the appearance of a small steam engine and costs about a thousand dollars. These batteries are specially made for the application.

Satellites designed with a life span of five years or less often use lithium-ion. A new breed of Li-ion is being developed that promises to last 18 years. This would satisfy most satellite requirements and replace the heavier nickel-based systems. The battery in development is a large 140Ah cell. Li-ion is lighter in weight, is easier to charge and has a lower self-discharge than the nickel-based toshiba satellite a350 battery systems of old. Furthermore, industrial versions of Li-ion promise to exceed the life span of nickel.

Low Voltage Cut-off

Li-ion batteries contain a protection circuit that shields the battery against abuse. This important safeguard has the disadvantage of turning the battery off if over-discharged. Storing a discharged battery for any length of time can do this. The self-discharge during storage gradually lowers the voltage of the already discharged battery and the protection circuit cuts off between 2.20 and 2.90V/cell.
Some battery chargers and analyzers, including those made by Cadex, feature a wake-up feature or “boost” to allow charging batteries that have fallen asleep. Without this feature, a charger would read these batteries as unserviceable and the packs are discarded. The boost feature applies a small charge current to activate the protection circuit to 2.20–2.90V/ cell, at which point a normal charge commences. Caution should be applied not to boost lithium-based batteries back to life that have dwelled below 1.5V/cell for a week or longer.Copper shunts may have formed inside the cells that can lead to a partial or total electrical short. If trying to recharge, such a damaged cell might become unstable, causing excessive heat or showing other anomalies.

Figure 1: Sleep mode of a lithium-ion battery Some over-discharged batteries can be “boosted” to life again. Discard pack if the voltage does not rise to a normal level within a minute while on boost.

A study of failed batteries done by Cadex reveals that three out of ten batteries die due to over-discharge. If serviced within a year or so, batteries that have fallen asleep can be revived without noticeable loss on performance. Lack of service squanders many good batteries, so much so that 90 percent of returned batteries have no fault and can be reused. The cellular industry estimates the cost of needless acer extensa 5220 battery replacement at $10 million a year. Refurbishing batteries has the added benefit of protecting the environment and keeping our planet green.