Giving Your Hybrid an Extra Charge

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Plug-In Conversions

Toyota Prius owners can double their mileage by ordering a kit that converts their vehicle into a plug-in hybrid.

Chris Cox of Derry, N.H., got tired of waiting for the electric car of the future. In August, he took matters into his own hands and had his 2008 Toyota Prius converted into a plug-in hybrid, which doubled its gas mileage — Cox now gets up to 100 miles per gallon for 30 to 40 miles at a stretch. Although the Prius is already a hybrid gas-electric model, the additional battery that Cox had installed enables him to travel more than 20 miles on all-electric power (compared to just two miles without it) before the gas engine kicks in.

Until now, such after-market auto modifications were the exclusive purview of fearless do-it-yourselfers (check out their work at EV Album or CalCars). But now many car dealers and repair shops will do the job for you — and consumers are lining up. Typically customers order the kits directly from one of a handful of makers, who in turn ship the components to an installer near you. At least for now, an after-market conversion is the only option if you really want to rev up your fuel economy — short of ditching your car altogether and plunking down $109,000 for the all-electric Tesla Roadster or settling for Zap's barely street-legal three-wheeler. "I wanted something real today," says Cox, 50, who works as a database administrator.

Don't expect a bargain, though: Conversion kits range anywhere from $5,000 for lead-acid batteries to more than $30,000 for lithium-ion technology. The more expensive kits buy you a longer all-electric range, don't need replacing as often, and take up less space. The catch is that the additional battery has to be recharged by plugging your car into an electric outlet for several hours every time the battery gets drained, which can be inconvenient. Cox paid $9,999 for a 207-lb. Hymotion lithium-ion battery module, which fits into the spare tire well behind the back seat of his Prius and takes about six hours to charge. Aside from the black rubber-capped electrical outlet installed on the rear left bumper, Cox's Silver Prius looks exactly as it did before the conversion. "I don't think I'll make the money back," admits Cox, who estimates that it will take 10 years to recoup the cost in saved gas. "I bought it so I could put the word out there and say, 'Hey, this is possible,'" he says.

Until now, the steep price of conversions and most car owners' lack of technical know-how have kept consumers at bay. And while the cost is still prohibitive for most folks, some of the safety concerns and technical hurdles have been alleviated. Hymotion's conversion kit comes with a three-year warranty and has been crash tested. Those worried about voiding their original warranty should know that it is illegal for a carmaker to do so solely because an after-market product has been installed. If that product causes any malfunction or damage to the factory-installed parts, however, the warranty won't cover the damage.

Hymotion, owned by A123 Systems and based in Watertown, Mass., has at least one advantage over its competitors: The company is one of two finalists being considered by General Motors to produce the lithium-ion battery for the Chevy Volt, which is widely expected to be the first commercially available plug-in hybrid in the U.S. when it goes on sale in 2010. (GM says the Volt will be able to travel up to 40 miles in all-electric mode before switching over to its gas or ethanol-powered engine.) But there are at least half a dozen other companies that sell conversion kits for the Prius, Ford Escape and other hybrid models.

Like Cox, many Americans are desperate to get better gas mileage, feel frustrated with fuel prices and are impatient with the pace of auto-makers' change. "Toyota could produce this [plug-in hybrid] in a heartbeat, but they are just not there yet," says Charles Tonelli, owner of Westboro Toyota in Westboro, Mass., which performed Cox's Prius conversion and has a waiting list of 96 other customers who want the same service. (Click here to see what's involved in a conversion). In the meantime, non-profits like CalCars and Plug In America are lobbying for tax credits and other incentives that may help speed adoption of the new technology. But if you can't wait until 2010 for a brand-new plug in, you can still get all charged up today.