Millions of inventions pass quietly through the U.S. patent office each year. Patent No. 7,033,406 did, too, until energy insiders spotted six words in the filing that sounded like a death knell for the internal combustion engine.

An Austin-based startup called EEStor promised "technologies for replacement of electrochemical batteries," meaning a motorist could plug in a car for five minutes and drive 500 miles roundtrip between Dallas and Houston without gasoline.

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By contrast, some plug-in hybrids on the horizon would require motorists to charge their cars in a wall outlet overnight and promise only 50 miles of gasoline-free commute. And the popular hybrids on the road today still depend heavily on fossil fuels.

"It's a paradigm shift," said Ian Clifford, chief executive of Toronto-based ZENN Motor Co., which has licensed EEStor's invention. "The Achilles' heel to the electric car industry has been energy storage. By all rights, this would make internal combustion engines unnecessary."

Clifford's company bought rights to EEStor's technology in August 2005 and expects EEStor to start shipping the battery replacement later this year for use in ZENN Motor's short-range, low-speed vehicles.

The technology also could help invigorate the renewable-energy sector by providing efficient, lightning-fast storage for solar power, or, on a small scale, a flash-charge for cell phones and laptops.

Skeptics, though, fear the claims stretch the bounds of existing technology to the point of alchemy.

"We've been trying to make this type of thing for 20 years and no one has been able to do it," said Robert Hebner, director of the University of Texas Center for Electromechanics. "Depending on who you believe, they're at or beyond the limit of what is possible."

EEStor's secret ingredient is a material sandwiched between thousands of wafer-thin metal sheets, like a series of foil-and-paper gum wrappers stacked on top of each other. Charged particles stick to the metal sheets and move quickly across EEStor's proprietary material.