Laptop, cell phone and iPod owners tired of having their devices run out of charge after a few hours have been patiently waiting for the next portable power source to arrive.

Tiny fuel cells, powered by combustible liquids or gasses, have long been touted as the eventual solution. Potentially, they could power a laptop for days between refills.

But fuel cells have perennially remained a year or two away from reaching the market as companies have worked on making them small, cheap and long-lasting, while making sure they do not overheat. The U.S. government removed a key roadblock this year when the Department of Transportation amended its hazardous materials regulations to allow cells with methanol, butane or formic acid to be carried on airplanes. Methanol and butane are flammable, and formic acid is corrosive.

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