Our Prius hybrid gets plugged in.(NEWS)(Product/service evaluation)

ONE OF THE ADVANTAGES of today's gas/electric hybrids is that they don't need to be plugged in to recharge their batteries. So why is there so much buzz about automakers over the next few years introducing plug-in hybrids, such as the Chevrolet Volt?

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By using larger or additional batteries, plug-in hybrids can run on electricity more of the time than conventional hybrids can, which means they use less gasoline. How much less? We had our 42-mpg Toyota Prius Touring model converted to a plug-in version and found that its gas mileage jumped to 67 mpg overall for the first 35 miles of driving, or until the added battery depleted its charge. That means that a driver with a relatively short commute could dramatically cut gas usage. And according to the Bureau of Transportation Statistics, 78 percent of Americans drive less than 40 miles per day to work and back.

In an era of volatile gas prices, that sounds appealing. But production plug-in cars won't be available to consumers before late 2010. And while some companies are converting current hybrids now, few drivers are likely to see the $10,875 conversion cost we paid as being worth it.

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In the conversion shop

For our Prius, we chose a Hymotion L5 conversion kit sold by A123 Systems, which the company claims can yield more than 100 mpg. The work was performed at a Toyota dealership in Massachusetts, one of seven U.S. venues that do that conversion.