Power to the Portables

It's surprising what you can make into a battery. For example, you can actually make a clock that runs on two potatoes. But when it comes to portable electronic devices, we generally stick to what we find at the local RadioShack.

Some batteries (called primary batteries) are thrown away, while others (secondary batteries) can be recharged and reused. Many devices, from flashlights to radios to some personal digital assistants (PDA), use alkaline batteries. Mercury cells power hearing aids and watches but pose a serious environmental threat. Alkaline cells once had significant mercury content, but current units use none.



The best-known rechargeable batteries are lead-acid: powerful, inexpensive, heavy and bulky—great for cars but little else. Also familiar are the rechargeable nickel-cadmium (Ni-Cad) batteries used in cell phones, handhelds, toys and portable tools. These relatively cheap cells can be recharged up to 1,500 times. Nickel metal hydride (NiMH) batteries, which are used in small mobile devices and inexpensive laptops, are environmentally safer than Ni-Cad but can be recharged only about one-third as many times.

Today, most laptops and cell phones use lithium-ion (Li-Ion) cells, which are three times as costly as NiMH cells but have high energy density. Li-Ion polymer batteries can be molded to fit inside mobile devices but are double the cost of Li-Ion cells.

Many experts feel that battery development has reached a plateau just when cheaper and more portable power sources are needed. Users would like a free, infinite power source weighing next to nothing; reality requires a removable power "brick" that can take hours to recharge batteries from a wall outlet. Devices are getting smaller, but faster CPUs and color displays drain power. So device makers are becoming increasingly reliant on software and hardware to lessen battery drain.

"Power is the big constraint today" on mobile computing, says Craig Mathias, an analyst at Farpoint Group in Ashland, Mass. Mathias says that although Moore's Law states that semiconductor processing power will double every 18 months, "a battery's effectiveness doubles every 50 years."

By fiddling with surface areas and voltages, IBM has been able to increase Li-Ion battery life for its ThinkPad X laptop from 3.8 hours to 4.6 hours.

Future Charges

IBM engineer Tom Hildner says he thinks that lithium batteries are "running out of steam" and that we need better chemistries. Many companies, including Electric Fuel Ltd. in New York, are focusing on power alternatives such as zinc-air cells. Others are trying fuel cells to power laptops, handhelds and cell phones.

While fuel cells might boost density, users would have to carry extra fuel in a cartridge. Hydrogen and methane, the most likely potential fuels, are flammable materials that aren't allowed on airplanes. Analysts say such fuel cells are years off because they're too expensive and dangerous.

One promising new technology is Li-Ion polymer phosphate, which is being promoted by Valence Technology Inc. in Austin, Texas. Called Saphion, this new battery uses environmentally friendly phosphate and promises to be half as costly as Li-Ion.

Bottom-line advice for IT shops: Give users spare laptop and cell phone batteries, plus recharging capability. Also, warn users that a device can lose data if power is lost for too long.

Rechargeable Batteries
Volts per cellEnergy density (Wh/kg)Battery discharge rateBattery lifePrice per cell Battery life (hours)Battery uses
Ni-Cad 1.2545Moderate to highUp to 1,500 charge/discharge cycles95 cents3Low-end: cordless phones, PDAs, handheld computers, portable hand tools, tape players and toys
NiMH 1.570ModerateUp to 500 charge/discharge cycles$1.502.4Midlevel: cordless phones, cell phones, laptops, PDAs, handheld computers and other portable devices
Li-lon1.0-3.6135LowUp to 1,000 charge/discharge cycles$43.2High-end: cordless phones, cell phones, laptops, PDAs, handheld computers and other portable devices
Li-lon polymer 1.0-3.6135LowUp to 1,000 charge/discharge cycles$83.7High-end: cell phones, laptops, PDAs, handheld computers and other portable devices
Li-lon polymer phosphate Not availableNot availableLowNot available$2-$33.88Potential for backup power systems, electric vehicles, cordless power tools and mobile electronic devices

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Copyright © 2002 IDG Communications, Inc.

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