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" When General Motors unveiled the Chevy Volt in January, plug-in hybrids suddenly seemed to matter again. Sure, the Volt is a concept car, and more of a testbed for various electric-drive systems than a showcase for plug-in charging. And the aftermarket kits that turn a Toyota Prius into a plug-in have been around for years. But with GM planning to build two plug-in vehicles -- the Volt, as well as its next Saturn Vue Green Line -- this technology is looking like the biggest thing since, well, hybrids.  + Click to enlarge  A plug-in Sprinter van (top) can get 20 gasfree miles; a kit-modified Prius can travel 31. (Photos by calcars.org)  How do plug-in hybrids work? Their batteries can be recharged either by the vehicle&amp;#039;s gasoline engine or the electric grid. A plug-in&amp;#039;s batteries are usually lithium-ion, which are more powerful than a standard hybrid&amp;#039;s nickel-metal-hydride batteries, but need to be plugged in for hours to fully charge. When the charge is depleted, the plug-in runs like a standard hybrid. How energy-efficient are they? Fully charging a kit-modified Toyota Prius adds around 50 cents to an electric bill, and the car has a battery-only range of 31 miles. Then the gas engine kicks in. Even so, a 100-mile trip burns just over 1 gal. of gasoline. Sounds like a bargain -- but keep in mind, the warranty-voiding kits cost up to $10,000. Why aren&amp;#039;t plug-ins in production? Automakers cite the high cost of lithium-ion batteries. Ford and Toyota have announced active interest in plug-ins, but for now they are sticking by their hybrids. DaimlerChrysler is currently testing a plug-in hybrid version of its Sprinter delivery van. Progress, maybe, but no one&amp;#039;s making production commitments. GM has taken the biggest leap, awarding contracts to battery makers to produce lithium-ion packs for its Saturn Vue Green Line. The more radically designed Chevy Volt -- which has a gas engine that recharges the batteries, and never powers the wheels -- will have to wait. It needs a 400-pound battery, which GM estimates won&amp;#039;t be feasible until 2012 at the earliest.  To learn more about the future of plug-in hybrids, check out the cover story in the May issue of Popular Mechanics, on newsstands soon!   TEST DRIVES: Ford HySeries Edge, Tesla Roadster, Hybrid Technologies L1X-75 Roadster  The Chevy Volt concept car has a 110-volt charging port on both sides of the front fender. It takes 6 hours to charge, and can travel 40 miles before burning gas. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/cars/a1412/4212941/>