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CNET's guide to laptop batteries
By Brian Nadel
26/04/2004 URL: http://asia.cnet.com/digitalliving/tips/0,3800004921,39176783,00.htm Dying for more juice? We'll help you extend your laptop's battery
life or choose an external battery to do the job.
One of your best options is an external laptop battery made by a third-party company. These devices weigh between 0.73kg and 1.5kg and range in cost from US$150 to US$500. In some cases, they can also power your cell phone or handheld device. If you don't mind lugging a few extra pounds, these batteries are easy to use because they simply plug into the notebook's AC power port and require no software. To gauge how well external batteries can get you through a long flight or a day at the beach, we rounded up four of the most-popular batteries and subjected them to a high-impact workout in CNET Labs. Pack one of these, and you'll never look at a wall outlet the same way again. But there's more to extending battery life than simply shelling out cash. To help you make smart decisions about the laptops you buy and the way you use them, we also demystify the various battery technologies and examine the fuel cell technology that might power your next laptop. We also give you 10 tips for getting the most out of your notebook's current battery, along with a glossary of key terms. We can't make a battery last forever, but we can help ensure that you get the most out of every electron. Paths to power Here's why lithium-ion batteries are the current power kings. Batteries vs. fuel cells Will fuel cells someday replace batteries? Power and performance We explain how the latest processors extend battery life. Ten tips for the power hungry How do you squeeze every minute of battery life out of your laptop? Glossary: how a battery works Get the scoop on how and why the electrons flow and learn the key battery terms. Paths to power: Five battery technologies explained
Although all batteries are not created equal, they all have the ability to turn chemical energy into electric current to power electronic devices, from tiny digital music players to big laptops. As with the battery in a car, a chemical reaction inside a laptop's battery frees electrons to flow from the positive terminal to the negative terminal, creating enough current to run the device. That was then The old-timer of mobile battery technologies is the nickel-cadmium cell (NiCd), once the mainstay of laptop design. Unfortunately, NiCd cells are able to carry enough power to run a laptop for only about an hour, and they contain toxic cadmium, which makes them hard to dispose of. And despite their ability to be recharged about 1,000 times, nickel-cadmium cell batteries also suffer from something called memory effects; over time, they lose the ability to hold a complete charge. Luckily, lighter and more powerful battery designs have surpassed the NiCd, and today, NiCds are used mostly in toys and inexpensive cordless phones. About a decade ago, most laptop makers switched to nickel-metal-hydride batteries (NiMH). Not only can these batteries hold about 40 percent more power, they aren't as susceptible to memory problems as NiCds are, and they are more environmentally friendly. On the downside, you can recharge them only about 200 times vs. 400 charge cycles for newer designs. Five battery
technologies
This is now Today, the lithium-ion cell (a.k.a. Li-ion), which holds roughly twice the capacity of a nickel-cadmium battery, rules the laptop battery roost. Used on most laptops, PDAs, and cell phones, lithium-ion technology can hold a lot of power, but its exotic materials make it expensive. Part of the credit for its success goes to a tiny controller chip embedded in each battery that adjusts how quickly the battery discharges and prevents it from overcharging. Coming soon Look for lithium-polymer (Li-poly) technology to make its way into cell phones, PDAs, and laptops in the near future. Extremely light and malleable, these batteries are capable of providing nearly as much power as lithium-ion cells but can also be shaped to fit into a device's hidden nooks and crannies. For a look at another battery technology, check out the next section on fuel cells. Batteries vs. fuel cells
So how does a fuel cell work? "The fuel cell is based on the reverse principle of water electrolysis...[Fuel cells] work by having hydrogen and oxygen react to generate electricity," said Yoshimi Kubo, senior research manager overseeing NEC's project to create a fuel cell-powered notebook (see picture of prototype). Methanol, or methyl alcohol, is NEC's fuel of choice, and Kubo has created a prototype laptop that can run for five hours on about a pint of 10 percent fuel. When the tank is dry, forget about a power cord, because the fuel cell wants more methanol. Just pour in a small bottle of fuel, and it's ready to go. Rather than carrying a bagful of batteries on a long flight, all you'd need is a bottle of methanol, but be careful: methanol is a poison. For now, packaging is the biggest obstacle that fuel cells face. "Currently, the fuel cell cannot fit into a standard battery location," Kubo said. "It will need further development in order to fit into a notebook, and miniaturization is a challenge we're facing." If all goes well, by year-end NEC may have a 2kg commercial notebook that runs for up to 40 hours on one tank of fuel. According to Kubo, NEC is attacking this problem from three directions: upping the concentration of methanol, using a low-power processor, and increasing the tank size. Fuel-cell-powered PDA By contrast, Hitachi is thinking smaller. Along with Tokai, a Japanese maker of cigarette lighters, Hitachi is working on a fuel cell-powered PDA. About the size of a AA battery, the fuel cell contains 2 ounces of 20 percent methanol fuel, and it powers a handheld computer for 6 to 8 hours. Before its planned launch next year, the companies will try to boost runtime by using 30 percent methanol fuel, making a 12-hour PDA a distinct possibility. All this adds up to big business over the next decade, according to Daniel Benjamin, a marketing analyst at Allied Business Intelligence, based in Oyster Bay, New York. "Fuel cells will provide a clean source of energy, but cost and technical issues will pose significant barriers." He has forecast the fuel-cell industry to be powering up with sales of only 5,000 units this year. But by 2011, there could be 200 million fuel cells of all sizes and capacities sold, powering everything from MP3 players to laptops. By then, we may be able to kiss our batteries good-bye, along with the eternal search for a power outlet to charge them--though finding fuel may create another problem. Power and performance
Now that you know how batteries work, here's the latest in processor technology. Even though the CPU consumes about half the laptop's total power, recent advances have changed the equation. Now, top laptop performance can go hand in hand with long battery life. You just have to know your CPUs.
Intel Pentium M (part of the Centrino package) Without a doubt, the Pentium M is the battery-life champ. With 77 million transistors, a megabyte of external cache, and the ability to streamline operations, it balances raw power with extensive battery life. Toss in an Intel-made Wi-Fi radio and an Intel chipset, and the Pentium M is part of the Centrino triad. Running at up to 1.7GHz, Pentium M laptops run rings around the competition, with an average MobileMark 2002 score of 152 and an average battery life of 4 hours, 12 minutes. Two new Pentium M-based designs are on the scene. First, the new Intel Celeron M uses the same computational core but half as much cache as the Pentium M and starts at US$107, making it the value alternative. By spring, you can expect a new generation of Pentium Ms that are smaller and faster. Code-named Dothan, these chips should boost battery life.
Intel Celeron M Based on the Pentium M, this new chip is an inexpensive alternative to the Pentium M. It runs at up to 1.2GHz and has 512MB of secondary data cache. With a 400MHz frontside bus, the Celeron M has the Pentium M's power-conservation software, which lets the CPU go into a deep sleep mode to cut consumption to a minimum. It's too early to tell what the chip's performance and battery potential will be. Mobile Intel Celeron The Mobile Celeron is based on the Pentium 4 core, is quite different from the Celeron M (despite the similar name), and uses more battery power. It runs from 650MHz to a top speed of 2.5GHz and supports frontside buses from 100MHz to 400MHz for a range of power and performance possibilities. Battery life is shorter than it is with laptops running a Pentium M. Intel Mobile Pentium 4 Based on the desktop Pentium 4, the Mobile Pentium 4 runs a little slower but has the same 55 million transistors and 512MB of external cache. This chip is used mostly on desktop-replacement laptops, and it can go as fast as 3.2GHz and costs as little as US$190. Based on testing of dozens of laptops, the average Mobile P4 notebook has a score of 121 on the MobileMark 2002 benchmark and can run for 2 hours, 47 minutes, which is much shorter than the Pentium M life.
Intel Pentium 4 This desktop-PC processor was originally found only on desktops, but it's now in some desktop-replacement laptops, as well. The Intel P4 is very fast and is less expensive than Mobile Pentium 4 and Pentium M chips, but it runs very hot and allows only poor battery life. AMD Athlon XP-M The Athlon XP-M uses AMD's QunatiSpeed and 3DNow technologies to speed up the most-used operations. With a top speed of 2GHz, the chips start at less than US$200. Athlon XP-M laptops average a MobileMark 2002 score of 99 and a runtime of 2 hours, 27 minutes, placing them behind Mobile Pentium 4 and Pentium M machines. A few laptops now feature AMD's 64-bit Mobile Athlon 64 processors. These laptops should be screamers, because they can chew through twice as much material in the same time compared to 32-bit Pentium and Crusoe processors. It's unclear so far how the chips affect battery life.
Transmeta Crusoe T-5800 By using Transmeta's code-morphing software, the Crusoe T-5800 off-loads some of the processor's toughest duties to software, which can save power. At a peak speed of 1GHz, the Crusoe T-5800 runs slower than the Athlon or Pentium chips and yields lower performance. Our averages show that the typical Crusoe laptop can run for 2 hours, 40 minutes, just behind the Mobile Pentium 4, but it lags on performance, with an average MobileMark 2002 score of 57. Transmeta's new chip, currently popular in Asian markets and just recently released in the United States, is called the Efficeon. The first laptop to use this processor in the United States is the Sharp Actius MM20, a 2-pounder that can run on batteries for more than 3 hours.
Apple PowerPC Apple iBook buyers get the slower 800MHz, 933MHz, and 1GHz PowerPC G4 processor, while those who upgrade to the faster PowerBooks will get speeds as fast as 1.33GHz. All of the PowerPC chips include 512KB of external cache. While the 12-inch iBook can run for about 3.5 hours, the higher-performing 17-inch PowerBook can go only 2.7 hours between charges, according to CNET Labs tests. Ten tips for the power hungry
1. Think small If extralong battery life matters to you, forget about that huge, 17-inch-screen laptop with the top-speed processor--it probably won't run for more than two hours. When you're buying your next laptop, think small and consider an ultraportable or a thin-and-light laptop. An Intel Pentium M processor uses about half as much power as a Pentium 4, a 12.1-inch screen uses 50 percent less juice than a 17-inch model, and getting a 4,200rpm hard drive instead of the 5,400rpm model can mean an extra 15 to 20 minutes of battery life. 2. Control your power Adjust your laptop's power settings to find a comfort zone where you're using as little power as possible with no interference in your computer tasks. The path to the control panel will vary according to your operating system and setup, but for Windows XP Home and Pro users, follow these steps: Go to Start > Control Panel > Performance And Maintenance > Power Options. Set the LCD screen to go off after 5 minutes of inactivity, let the hard drive stay active for 20 minutes, and store the system's contents in RAM when it shuts down. If your laptop goes to sleep too soon, adjust the settings.
3. Dim all the lights Your LCD's backlight uses up to 10 watts of power, a huge battery drain. Lower the screen's brightness to where it's comfortable to view without squinting. In addition to the Power Options settings detailed in tip 2, most laptops have convenient function keys for controlling brightness. Look for the function key with the brightness icon and a down arrow next to it. (This is the F6 key on many laptops.) Also, some new laptops, such as the Apple 17-inch PowerBook, adjust the screen's brightness to suit the conditions. 4. Be battery smart Know how much power remains by checking the battery power icon in the system tray. Or buy a laptop with a battery that features a charge-level LED gauge on the battery itself so that you can just flip over the notebook to see how much battery life remains. If you really want to see tons of detail on what your battery is doing and how much life is left, take battery monitoring to the next level with PassMark's US$15 BatteryMon 1.3 program. 5. Double or triple your pleasure Some laptops, such as Fujitsu's LifeBook S series, let you double up with a second battery that fits into a modular bay, nearly doubling runtime. A few laptops can even take as many as three batteries, if you include the docking station, also called a media slice. The IBM ThinkPad X40, for instance, can be fitted with a large-capacity battery in place of its standard battery, and it has a connector for an additional bottom-mounted external battery. 6. Charge when you can Before leaving the home or the office with your laptop, fully charge all of your batteries. If you're traveling, look around for a wall outlet to give your batteries a refresher charge when you can, because every little bit helps. Some third-party devices will help you charge on the road, such as iGo's Juice 70 (US$120). This versatile device does it all: it's a regular AC adapter, as well as a car converter, and it will work on many airplanes. With the right plug, it can even charge your phone or PDA. 7. Check the CMOS battery If you have to reset your laptop's clock or your system BIOS, you may have a bad backup battery. Also called the CMOS battery, this secondary battery, which powers the clock when the system is not in use, can sap the main battery power if it's dead. The good news is that this battery is inexpensive. The bad news is that you'll likely have to dig around inside the laptop to find it. Some vendors put the backup battery under the memory chip slots, while others stash the CMOS battery under or next to the main battery. Check your manual or the vendor's technical support Web site for details. 8. Shut down unnecessary programs When you're running your laptop on battery power, turn off devices and programs you don't need. When not connected to a wireless hot spot, turn off the Wi-Fi hardware. If you access wireless networks with a PC Card, remove it when not connected. Listening to music via the CD-ROM drive and watching DVDs are also big battery drains. 9. Start with complete battery drains To ensure long-term battery vitality, do the following: When first using your laptop on battery power, let the battery completely drain before you recharge it. Don't recharge when the battery is only half drained. Do that for at least the first two sessions. Also, avoid temperature extremes. Don't leave a laptop in a hot car or use it outdoors in extremely cold weather; hot batteries discharge very quickly, and cold ones can't create as much power. 10. Terminal care Make sure the battery contacts that connect your cells to the laptop are straight and clean and free of grime, because the last thing you need is a bad connection. Most contacts are flat, copper-colored metal strips, but they might be hidden between pieces of protective plastic. Every six months or so, give the contacts a cleaning with a cotton swab and rubbing alcohol to remove electron-sapping dirt and grime. A bad connection can keep you from getting the most out of a battery. Glossary: how a battery works
Battery cell Cells are individual cylindrical compartments in a battery that produce power. As many as 12 cells are used in a laptop battery. Capacity This refers to the amount of energy a battery contains. The typical laptop battery has between 2,000 and 6,000 milliamp hours (mAh) of capacity. See milliamp hours. Charge cycle This describes the complete charge and discharge cycle of the battery. Fully draining the battery then recharging it is one charge cycle. Degradation The process by which the chemicals in a battery lose their ability to hold a full charge. See memory effect. Discharge This describes using the power stored in a battery by chemically depleting the charge. Electrolyte This chemical carries electrons while the battery is being used. Energy density This term describes how much energy a battery contains, based on its watt-hour capacity divided by its weight; many external batteries have between 100 and 200 watt-hours of energy. Fuel cell This refers to any of various devices that convert chemical energy directly into electrical energy. They are different from batteries because they use liquid fuel to produce electrical energy, whereas batteries use reversible chemical reactions. Lithium-ion battery These batteries use lithium for the negative electrode and offer high energy density and the ability to undergo repeated charge cycles. Lithium-ion-polymer battery Similar to a lithium-ion battery, a lithium-ion-polymer battery uses a conductive plastic and is more malleable than traditional lithium-ion batteries. Lithium-ion polymer can be molded into different shapes, which can be critically important to the makers of small devices, such as cell phones. Memory effect (a.k.a. memory degradation) Not to be confused with computer memory, this is the loss of the ability to fully recharge a battery, which happens over a long period of battery use. Milliamp hour This is the main battery capacity rating, equal to one-thousandth of an amp-hour, generally referred to by its acronym: mAh. The typical laptop battery has between 2,000 and 6,000 milliamp hours of capacity. Negative electrode This is the conductive part of the battery to which electrons flow. Nickel-cadmium battery Also known as NiCd, this is the original battery technology used in laptops. In using cadmium as the negative electrode, these batteries have a relatively low energy density and suffer from memory effects. Nickel-metal-hydride battery By removing the cadmium and using nickel hydride instead, these batteries are made to hold more energy, but they can't be recharged more than a few hundred times. They are generally referred to as NiMH. Porous separator This permeable material or membrane separates the battery's two electrodes and allows current to flow from the positive to the negative electrode. Positive electrode This is the conductive part of the battery; electrons flow away from it. Rechargeable battery This is a battery that can be used repeatedly by adding power to it when the cells are drained. These batteries typically can go through a few hundred charge cycles before they start to lose the ability to hold a charge. Watt-hour A watt-hour is a measurement of the amount of energy held in a battery that can power a one-watt device for one hour. Many external batteries have between 100 and 200 watt-hours of energy. How we test external laptop batteries
To start, each external battery is charged completely and checked for the correct voltage. We then connect the external battery to the laptop with the supplied AC power adapter and let the battery discharge by running the Satellite Pro 6100 connected to a Wi-Fi wireless network with Internet Explorer tuned to an Internet radio station. All power conservation software is disabled. We monitor the test's progress with PassMark's BatteryMon program. All tests are repeated three times, and we average the results. When the tests finish, we plug the external battery into an outlet and time how long it takes to recharge. While the best external batteries we tested provide an extra 4 hours of power, your mileage will vary depending on your laptop and hardware and what programs you're running. With a long-lasting, low-power laptop or a tablet PC, such as the Electrovaya Scribbler SC-2000, the external battery may add an extra 10 hours or more of battery life. |
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