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.

The Best Rechargeable Batteries and Chargers Of 2011

Today, the best rechargeable batteries are the new hybrid Nickel-Metal Hydride (Ni-MH) cells. These hybrid batteries have a lot going for them: they come fully charged (like alkaline batteries), and they can hold their charge over may months (unlike regular Ni-MH rechargeables). Because they can hold their charge for so long, they are suitable for low-drain devices like remote controls and flashlights. But they are also ideal for use in high-drain electronic devices like digital cameras.

So, basically, these new hybrid Ni-MH cells offer the convenience and shelf-life of alkalines, and the high-drain performance of older Ni-MH batteries. Here’s a list of the hybrid batteries available: Eneloop, E8DE 1000 and Hybrio.

If, however, being able to recharge batteries quickly is your priority, you may want to look at Rayovac’s IC3 Ni-MH batteries, which have the advantage of being able to be recharged in 15 minutes (see more information below).

We also review some of the best battery chargers at the end of this article.

Eneloop Rechargeable Batteries by Sanyo

Eneloop batteries are Ni-MH batteries made by Sanyo in Japan. Sanyo says Eneloops can be recharged up to 1000 times, and they will retain their charged capacity even after 6 or 12 months of storage. (According to Sanyo the specs are: 90% of charged capacity retained after 6 months, and 85% capacity after 12 months at 20 degree Celsius). The AA-sized (R6) batteries are rated at 2000 mAh, and the AAA-sized (R03) cells are rated at 800 mAh. A pack of four AA Eneloops costs about $12. The charge times are as follows: AA Eneloops charge in 230 minutes, and AAA Eneloops charge in 135 minutes.
You can get packs of Eneloop batteries from Amazon.

Eneloop batteries are also available with a USB Charger, or a Universal Charger with 8 Eneloop Batteries included.

E8GE 1000 Hybrid Rechargeable Batteries

E8GE Rechargeable Hybrid Batteries

The E8GE 1000 batteries are the newest hybrid batteries to be introduced, and they are also the highest rated at 2100 mAh (this stands for milli Amp hour, and indicates a battery’s energy storage capacity). Eneloops, by comparison, have a lower rated capacity — 2000 mAh (or 1980 mAh according to my informal tests).

E8DE batteries are rechargeable up to 1000 cycles, and they are “ultra-low self-discharging” batteries.
E8GE 1000 batteries are available from Amazon.

Hybrio Rechargeable Batteries by Uniross

Uniross, a French acer battery company, Ni-MH battery called the Hybrio. Like disposable alkaline batteries, they come fully charged when you buy them. Hybrios are said to keep 70% of their charge after a year.
You can recharge the Hybrios in any standard Ni-MH charger, and they can be recharged up to 500 times. A pack of four Hybrio cells costs about $12. The AA-sized Hybrios are rated at 1900 mAh. Uniross offers a three year limited warranty on these cells. They are also branded as: Ultralast, Again and Again, and Uniross.

Hybrio batteries are available from Amazon

I-C3 Rechargeable Batteries by Rayovac

In 2004, Rayovac introduced a new line of Ni-MH batteries called I-C3s, that can be recharged in 15 minutes. The I-C3 term stands for “In-Cell Charge Control”, meaning the cells have some circuitry inside them that assists with recharging, allowing for a much quicker charging time. Rayovac says the cells can be recharged “up to a thousand times”. The AA sized batteries are rated at 2000mAh. A four pack of the AA-sized batteries costs about $10. Unfortunately, Rayovac has discontinued these batteries in favor of their own line of hybrid Ni-MH batteries.

I-C3 batteries come with a special charger that features a cooling fan to keep the batteries from getting too hot during the fast charging. There are two charger models: the PS6, which can charge four AA or AAA batteries, and comes with a plug-in 110-120V AC power supply (or optionally, a 12V DC car cord). The PS5 charger model can charge two AA or AAA batteries, and plugs directly into a wall outlet. The PS5 can be used in countries with 220V using an adapter for the outlet.

Ordinary Ni-MH and Ni-CD type batteries can be charged in the I-C3 chargers, but it will act like an overnight charger with these batteries.
Rayovac IC3 Batteries are available from Amazon.

Best Battery Chargers

How about some good battery chargers to go with these batteries?
The chargers featured below are some of the smartest out there — they have built-in protection to prevent overcharging or undercharging. They can also handle most battery sizes.

LaCrosse Technology BC-900 Alpha Battery Charger and Recovery System

The LaCrosse Alpha Charger is a “smart” charger. It has sophisticated monitoring circuitry that controls the charging process, and it is also capable of “renewing” batteries by running full controlled discharge-recharge cycles.

The charger shows acer extensa 5220 battery voltage and charge status on its digital display. It has four separate charge channels so you can charge one, two three or four batteries at a time – even on individual charge programs. This allows you to test one battery while charging the others. It comes with four AA and four AAA batteries, four battery adapters (which convert AA sized battery to C and D sizes) and a carry case. It available from Amazon for about $40.
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Ansmann Deluxe “Energy 16″ Charger

Ansmann is a German company known for their range of high-end, intelligent battery chargers. Ansmann’s “Energy 16″ charger can handle both NiCad and NiMH (Nickel Metal Hydride) rechargeable batteries. When the batteries are inserted into the charger, they are analysed, and batteries needing reconditioning are automatically restored by several cycles of charging and discharging. The charger will also indicate if a acer aspire 5536 battery has been damaged and cannot be charged.

This charger has ten charging positions: six for AAA, AA, C or D sized cells, and four for 9V cells. The six top positions can handle two AAA or two AA cells or one each of the larger C or D cells.
A LED display shows the state of charging for each cell.

This charger can be used worldwide — it accepts 100-240V 50-60Hz AC.
It’s available from Amazon for around $120.

Ansmann Deluxe “Energy 8″ Charger

Ansmann’s “Energy 8″ charger has all the features of the “Energy 16″ charger, but has 8 charging points instead of 16. It has four AAA/AA/C/D and two 9V positions.
It’s available from Amazon for around $70.

Maha PowerEx “Ultimate Professional” Charger

The Maha’s Ultimate Professional Charger almost lives up to its hyperbolic name. This compact charger can charge any combination of 1 to 8 batteries. You can mix and charge AA, AAA, C and D sized cells at the same time on individual charging circuits. Each acer aspire 5920 battery size also has its own fixed contact charging points (i.e. not a spring). An LCD display shows charging and conditioning status of each rechargeable battery.

Like the Ansmann chargers, Maha’s chargers can restore batteries to their optimal performance level by repeatedly charging and discharging them. It also has intelligent charging technology and overcharge protection. It also comes with an international AC adapter, and short-circuit protection.

What is the C-rate?

In the late 1700s, Charles-Augustin de Coulomb ruled that a battery that receives a charge current of one ampere (1A) passes one coulomb (1C) of charge every second. In 10 seconds, 10 coulombs pass into the battery, and so on. On discharge, the process reverses. Today, the battery industry uses C-rate to scale the charge and discharge current of a battery.

Most portable batteries are rated at 1C, meaning that a 1,000mAh battery that is discharged at 1C rate should under ideal conditions provide a current of 1,000mA for one hour. The same battery discharging at 0.5C would provide 500mA for two hours, and at 2C, the 1,000mAh battery would deliver 2,000mA for 30 minutes. 1C is also known as a one-hour discharge; a 0.5C is a two-hour, and a 2C is a half-hour discharge.

The battery capacity, or the amount of energy a battery can hold, can be measured with a battery analyzer. The analyzer discharges the battery at a calibrated current while measuring the time it takes to reach the end-of-discharge voltage. An instrument displaying the results in percentage of the nominal rating would show 100 percent if a 1,000mAh test battery could provide 1,000mA for one hour. If the discharge lasts for 30 minutes before reaching the end-of-discharge cut-off voltage, then the battery has a capacity of 50 percent. A new battery is sometimes overrated and can produce more than 100 percent capacity; others are underrated and never reach 100 percent even after priming.

When discharging a battery with a battery analyzer capable of applying different C‑rates, a higher C‑rate will produce a lower capacity reading and vice versa. By discharging the 1,000mAh battery at the faster 2C, or 2,000mA, the battery should ideally deliver the full capacity in 30 minutes. The sum should be the same as with a slower discharge since the identical amount of energy is being dispensed, only over a shorter time. In reality, internal resistance turns some of the energy into heat and lowers the resulting capacity to about 95 percent or less. Discharging the same battery at 0.5C, or 500mA over two hours, will likely increase the capacity to above 100 percent.

To obtain a reasonably good capacity reading, manufacturers commonly rate lead acid at 0.05C, or a 20-hour discharge. Even at this slow discharge rate, the battery seldom attains a 100 percent capacity. Manufacturers provide capacity offsets to adjust for the discrepancies in capacity if discharged at a higher C‑rate than specified. Figure 1 illustrates the discharge times of a lead acid battery at various loads as expressed in C-rate.

Figure 1: Typical discharge curves of lead acid as a function of C-rate
Smaller batteries are rated at a 1C discharge rate. Due to sluggish behavior, lead acid is rated at 0.2C (5h) and 0.05C (20h).

While lead- and nickel-based batteries can be discharged at a high rate, a safety circuit prevents Li-ion with cobalt cathodes from discharging above 1C. Manganese and phosphate can tolerate discharge rates of up to 10C and the current threshold is set higher accordingly.

Comparing the Battery with other Power Sources

This article begins with the positive traits of the battery, and then moves into the limitations when compared with other power sources.

Energy storage
Batteries store energy well and for a considerable length of time. Primary batteries (non-rechargeable) hold more energy than secondary (rechargeable), and the self-discharge is lower. Alkaline cells are good for 10 years with minimal losses. Lead-, nickel- and lithium-based batteries need periodic recharges to compensate for lost power.

Specific energy (Capacity)
A laptop battery may hold adequate energy for portable use, but this does not transfer equally well for large mobile and stationary systems. For example, a 100kg (220lb) battery produces about 10kWh of energy — an IC engine of the same weight generates 100kW.

Responsiveness
Batteries have a huge advantage over other power sources in being ready to deliver on short notice — think of the quick action of the camera flash! There is no warm-up, as is the case with the internal combustion (IC) engine; the power from the battery flows within a fraction of a second. In comparison, a jet engine takes several seconds to gain power, a fuel cell requires a few minutes, and the cold steam engine of a locomotive needs hours to build up steam.

Power bandwidth
Rechargeable batteries have a wide power bandwidth, a quality that is shared with the diesel engine. In comparison, the bandwidth of the fuel cell is narrow and works best within a specific load. Jet engines also have a limited power bandwidth. They have poor low-end torque and operate most efficiently at a defined revolution-per-minute (RPM).

Environment
The battery runs clean and stays reasonably cool. Sealed cells have no exhaust, are quiet and do not vibrate. This is in sharp contrast with the IC engine and larger fuel cells that require noisy compressors and cooling fans. The IC engine also needs air and exhausts toxic gases.

Efficiency
The battery is highly efficient. Below 70 percent charge, the charge efficiency is close to 100 percent and the discharge losses are only a few percent. In comparison, the energy efficiency of the fuel cell is 20 to 60 percent, and the thermal engines is 25 to 30 percent. (At optimal air intake speed and temperature, the GE90-115 on the Boeing 777 jetliner is 37 percent efficient.)
Installation

The sealed battery operates in any position and offers good shock and vibration tolerance. This benefit does not transfer to the flooded batteries that must be installed in the upright position. Most IC engines must also be positioned in the upright position and mounted on shock- absorbing dampers to reduce vibration. Thermal engines also need air and an exhaust.

Operating cost
Lithium- and nickel-based batteries are best suited for portable devices; lead acid batteries are economical for wheeled mobility and stationary applications. Cost and weight make batteries impractical for electric powertrains in larger vehicles. The price of a 1,000-watt battery (1kW) is roughly $1,000 and it has a life span of about 2,500 hours. Adding the replacement cost of $0.40/h and an average of $0.10/kWh for charging, the cost per kWh comes to about $0.50. The IC engine costs less to build per watt and lasts for about 4,000 hours. This brings the cost per 1kWh to about $0.34. Read more about the Battery Against Fossil Fuel.

Maintenance
With the exception of watering of flooded lead batteries and discharging NiCds to prevent "memory," rechargeable batteries require low maintenance. Service includes cleaning of corrosion buildup on the outside terminals and applying periodic performance checks.

Service life
The rechargeable battery has a relatively short service life and ages even if not in use. In consumer products, the 3- to 5-year lifespan is satisfactory. This is not acceptable for larger batteries in industry, and makers of the hybrid and electric vehicles guarantee their batteries for 8 to 10 years. The fuel cell delivers 2,000 to 5,000 hours of service and, depending on temperature, large stationary batteries are good for 5 to 20 years.

Temperature extremes
Like molasses, cold temperatures slow the electrochemical reaction and batteries do not perform well below freezing. The fuel cell shares the same problem, but the internal combustion engine does well once warmed up. Charging must always be done above freezing. Operating at a high temperature provides a performance boost but this causes rapid aging due to added stress. Read about Discharging at High and Low Temperatures.

Charge time
Here, the battery has an undisputed disadvantage. Lithium- and nickel-based systems take 1 to 3 hours to charge; lead acid typically takes 14 hours. In comparison, filling up a vehicle only takes a few minutes. Although some electric vehicles can be charged to 80 percent in less than one hour on a high-power outlet, users of electric vehicles will need to make adjustments.

Disposal
Nickel-cadmium and lead acid batteries contain hazardous material and cannot be disposed of in landfills. Nickel-metal-hydrate and lithium systems are environmentally friendly and can be disposed of with regular household items in small quantities. Authorities recommend that all batteries be recycled.

IE9 Best Browser For Laptop Battery Life

IE 9 looks set to roll out to users via the Windows Update in late June and for many that could see improvements in their laptop battery life performance, at least that’s if the latest tests from Microsoft are true. Some may consider this a biased study since Microsoft carried out the tests, and inevitably IE came out on top.

However, I’m going to be the middle man in this case, and assume that the test was carried out fairly. Microsoft compared Internet Explorer 9, their latest browser with Opera 11, Firefox 4, Chrome 10 and Safari 5 on an Intel powered laptop. They then measure just how many watts the machine consumed with the browser idling, showing a news site and then running some graphic intensive web tasks.
The results? Well Internet Explorer came out as the most efficient web browser.


Obviously Microsoft were proud of this achievement, as IE 9 is said to be a big change from it’s predecessors, and that it is.toshiba laptop battery

However there is plenty of factors which could affect the result. The tests were carried out on a Windows 7 machine with an Intel chip, both of which Internet Explorer is designed to run best on. If you we’re to try Safari on the Mac, a platform which Safari is optimised to run on, I think you could find some different results.

Also the test sites that Microsoft used may not be ones anyone else would care to use and all laptops have different rates of power consumption, in fact there is an awful lot of variables in this test which aren’t factored in.

In fairness to Microsoft though, we appreciate you for caring about power consumption and the environment, and I’m sure we’d all love to have a bit of extra dell battery life from our laptops

Laptop Battery Is Indeed Too Good to Be True

The technology is actually quite fascinating. It’s a “betavoltaic” power source. These actually exist. And they work by getting together a lump of radioactive material battery(like tritium) that emits beta particles and then converting the beta particles to electricity. It’s just like photovoltaics…except instead of photons, it’s beta particles.

This device isn’t a battery, it’s actually a power source, and it will indeed continue producing power for 30 years (the half-life of tritium is 12 years, so it will be producing roughly 25% of its power 30 years from now.) But the article doesn’t point out that there are significant problems with the technology, specifically when using it as a laptop battery such as a dell laptop battery.

So what are the problems?
1. To power a laptop, you’d need about 50 lbs of tritium. Researchers plan on surmounting this by trickle charging a battery with the betavoltaic. This way, when the laptop is not in use, the battery would be recharged by the betavoltaic power source. But while using the laptop, you’d experience nothing more than an increase in life…not a 30 year battery.

2. While the article states that these laptops would run cooler than Li-ion laptops, that’s quite wrong. Betavoltaics lose about 75% of their energy as heat, and as designers will be required to include Li-ion batteries anyway, I imagine, if anything they’d be hotter.

3. At the end of its, life the power source would be completely innert, but during use, it wouldn’t be. Moderate shielding can easily block beta waves, but if the battery were damaged, and then you placed it on your “lap” I would hate to think of the consequnces. I’m not saying that this technology isn’t useful. In fact, it’s very useful, particularly for space missions requiring low but constant power. Or for any device that needs a low voltage for a long period of time and is difficult to access.

The possibility of trickle charging a Li-ion battery for increased life is intriguing, and certain low-power cell phones may someday be able to run 100% on betavoltaics. But a 30-year laptop battery, I’m afraid, doesn’t look likely.