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The retrofitted plug-in hybrid is still far from mass production, however. Mark Verbrugge, director of the Materials and Processes Laboratory at GM, says developing a new kind of car costs about a billion dollars, so automakers want to be sure that it will actually sell. In the past, attempts to introduce electric vehicles have not been commercial successes. The primary concerns about plug-in vehicles include the cost of the system and the safety and lifetime of the large battery packs. Electro Energy’s Klein estimates that the company’s batteries will need to be replaced every five years – well short of the 10 to 15 years automakers think would appeal to consumers.

Electro Energy engineers replaced the nickel-metal hydride battery used in the Prius with a battery using the same chemistry, but assembled in a much simpler, more compact way. Klein estimates that if automakers were to integrate the new batteries into cars from the beginning, the cars would cost about $5,000 more than a conventional car. As it is, the conversion kits will add $5,000 to the cost of a Prius, which already sells for thousands more than a conventional car in the same class. Electro Energy plans to retrofit more demonstration cars in the next 12 months, with the possibility of ramping up production to thousands of units in the following year.

Another company developing plug-in electrics is EnergyCS of Monrovia, CA, which uses lithium-ion batteries developed by Valence Technology of Austin, TX. Lithium-ion batteries currently cost more than nickel-metal hydride ones, but they’re lighter, which could increase efficiency. The company is marketing the system through EDrive Systems of Los Angeles and plans to start retrofitting Priuses for under $12,000. A Toronto company, Hymotion, expects to offer consumers plug-in hybrid kits for a variety of hybrids by later this year; the Prius kit will cost about $9,500.

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