Mobile computing's energy crisis

Battery technology hasn't kept up with twin demands of taking up less space and powering more features in disconnected computing devices.

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Portable Power Alternatives

PROS CONS
Nickel cadmium (NiCd) Can deliver high levels of power at a very low cost and recharges quickly. Low energy density; suffers from memory effect that can cut battery life if battery isn't maintained properly. Cadmium batteries are environmentally unfriendly and likely to be phased out.
Nickel metal hydride (NiMH) Supports high-discharge rates well; delivers more power for its size than NiCd; no memory-effect issues. Lasts for 300 to 500 charge cycles vs. 1,500 for NiCd.
Lithium ion Combines high energy density and light weight. No memory-effect issues. Same cycle life as NiMH. Relatively expensive. Volatile chemistry requires special safety mechanisms and strict manufacturing controls.
Lithium ion polymer Same characteristics as lithium ion but can be molded into very thin shapes. More expensive than traditional lithium ion.
Reusable alkaline Discharge rate is low when not in use: 0.3% per month vs. 10% for lithium ion and 30% for NiMH. Limited to about 50 charge cycles vs. 300 to 500 for lithium-based batteries.
Direct methanol fuel cells Long run times, which can be extended by refueling the device. Still at prototype stage; mature products not expected before 2010. Complex to build. Inefficient process generates waste heat; reacts too slowly to peak load demands.

Source: Cadex Electronics Inc., Richmond, British Columbia

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Fuel Cell
A Traditional Battery vs the Fuel Cell

Batteries use an electrochemical process that generates current through the interaction of two chemicals: one that gives up electrons and another that accepts them. Batteries consist of three basic elements: the anode (negative electrode), cathode (positive electrode), electrolyte fluid and a separator. By modifying the materials used in these elements, companies hope to create a new battery with a substantially higher energy density.

A traditional battery cylinder (inset, left) generates power from a cell winding containing two chemicals separated by a specialized membrane used to control the reaction. A fuel cell also uses a membrane to separate the air/methanol fuel mix, but also requires a fuel tank and special electronics to control fuel flow. MTI's Mobion unit (inset, right) is small enough to be used to power a PDA.
A Traditional Battery vs the Fuel Cell

Source: Valence Technology Inc., MTI MicroFuel Cells Inc.

Copyright © 2005 IDG Communications, Inc.

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