Ever wondered why your portable device's battery doesn't last longer? We explain the technology behind battery power, and provide tips on how to maximise it.

The simple fact of notebook life is that systems simply don't run for as long on their batteries as we'd like -- even long-lived notebooks, such as IBM's ThinkPad X31, last only 8 hours on two batteries.

To help you make smart decisions about the notebooks you buy and the way you use them, we demystify today's battery technologies and examine the fuel cell technology that might power your next notebook. We also provide 10 tips for getting the most out of your system's current battery, along with a glossary of key terms.

We can't make a battery last forever, but we can help to make sure that you get the most out of every electron.

With four battery technologies onstage and one waiting in the wings, there's sure to be a battery to suit your needs.

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 notebooks. As with the battery in a car, a chemical reaction inside a notebook'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 notebook design. Unfortunately, NiCd cells can only carry enough power to run a system for 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 notebook 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 versus 400 charge cycles for newer designs.

This is now
Today, the lithium-ion cell (also known as Li-ion), which holds roughly twice the capacity of a nickel-cadmium battery, rules the notebook battery roost. Used on most notebooks, handhelds, and mobile 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 mobile phones, handhelds and notebooks 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.

The traditional battery's days may be numbered. Thanks to recent advances in fuel-cell technology, your next notebook (or maybe the one after that) could run for days on a single charge. These next-generation batteries, which contain chemicals such as methanol stored in small tanks, certainly aren't your average power source. More like tiny chemical plants, different types of fuel cells are currently used in space shuttles, experimental eco-friendly cars and small power plants. NEC is developing a fuel cell for a notebook that could provide a mind-boggling 40 hours of battery life.

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 (prototype pictured above).

Methanol, or methyl alcohol, is NEC's fuel of choice, and Kubo has created a prototype notebook that can run for five hours on about a pint of 10 percent fuel. When the tank is dry, forget about a power cable, 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 miniaturisation is a challenge we're facing". If all goes well, by the end of 2004 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 handheld
By contrast, Hitachi is thinking smaller. Along with Tokai, a Japanese maker of cigarette lighters, Hitachi is working on a fuel cell-powered handheld. About the size of a AA battery, the fuel cell contains 57g 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 handheld 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 notebooks.

By then, we may be able to kiss our batteries goodbye, along with the eternal search for a power outlet to charge them -- although finding fuel may create another problem.

The notebook you buy may help determine the amount of uptime you can expect on an air flight. How come? Even though the CPU consumes about half the notebook's total power, recent advances in processor technology have eased the burden placed on a system's battery. Now, thanks to Intel's Pentium M and Centrino technology, for instance, notebooks can run faster and longer on the same batteries they used to use. Here's the low-down on which processors let notebooks last the longest.

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 Level 2 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 notebooks run rings around the competition, with an average MobileMark 2002 score of 152 and an average battery life of 4 hours and 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. Soon, you can expect a new generation of Pentium Ms that are smaller and faster: codenamed 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 Level 2 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 notebooks 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 Level 2 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 notebooks, the average Mobile Pentium 4 notebook has a score of 121 on MobileMark 2002 and can run for 2 hours and 47 minutes, which is much shorter than the average for Pentium M systems.

Intel Pentium 4
This desktop-PC processor was originally found only on desktops, but it's now in some desktop-replacement notebooks, as well. The Intel Pentium 4 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 QuantiSpeed 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 notebooks average a MobileMark 2002 score of 99 and a runtime of 2 hours and 27 minutes, placing them behind Mobile Pentium 4 and Pentium M systems.

A few notebooks, including Acer's Aspire 1500 range, now feature AMD's 64-bit Mobile Athlon 64 processors. These systems 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 these 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 Athlon or Pentium chips and yields lower performance. Our averages show that the typical Crusoe notebook can run for 2 hours and 40 minutes, just behind the Mobile Pentium 4; however, 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 US, is called the Efficeon. The first notebook to use this processor in the US is the Sharp Actius MM20, a sub-1kg system 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 Level 2 cache. While the 12in. iBook can run for about 3.5 hours, the higher-performing 17in. PowerBook can go only 2.7 hours between charges, according to our tests.

With a little power conservation and some smart moves, you can greatly improve your notebook's battery life. Here are our top 10 tips for getting the most out of your batteries.

1. Think small

If extra-long battery life matters to you, forget about that huge, 17in.-screen notebook with the top-speed processor -- it probably won't run for more than two hours. When you're buying your next notebook, think small and consider an ultra-portable or a thin-and-light system. An Intel Pentium M processor uses about half as much power as a Pentium 4, a 12.1in. screen uses 50 percent less juice than a 17in. model, and getting a 4,200rpm hard drive instead of a 5,400rpm model can mean an extra 15 to 20 minutes of battery life.

2. Control your power

Adjust your notebook's power settings to find a comfort zone where you're using as little power as possible with no interference in your computing 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 notebook 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 above, most notebooks have convenient function keys for controlling screen brightness. Look for the function key with the brightness icon and a down arrow next to it (this is the F6 key on many systems). Also, some new notebooks, such as Apple's 17in. 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 notebook with a battery that features a charge-level LED gauge on the battery itself so that you can just flip over the system 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 BatteryMon utility.

5. Double or triple your pleasure

Some notebooks, 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 systems 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 notebook, fully charge all of your batteries. If you're travelling, 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. 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 handheld.

7. Check the CMOS battery

If you have to reset your notebook'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 system 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 notebook 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 notebook 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 notebook 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 notebook are straight and clean and free of grime, because the last thing you need is a bad connection. Most contacts are flat, copper-coloured 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.

Battery cell
Cells are individual cylindrical compartments in a battery that produce power. As many as 12 cells are used in a notebook battery.

Capacity
This refers to the amount of energy a battery contains. The typical notebook 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 moulded into different shapes, which can be critically important to the makers of small devices, such as mobile 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 notebook 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 notebooks. 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.