"The Hymotion plug-in conversion kit holds the most energy, but is the most expensive."
“That Bible for smart shoppers, Consumer Reports—whose new-car reliability ratings are hugely influential—took a leap into the future in its February issue. It tested a Toyota Prius that had been converted to a plug-in hybrid, using the Hymotion L5 conversion kit sold by A123 Systems of Watertown, Massachusetts.
Did the no-nonsense, grimly methodical magazine give the plug-in a thumbs-up? As usual, the testers focused on the numbers. While Hymotion claims their kit can return up to 100 miles per gallon, CR’s Auto Test Center in East Haddam, Connecticut, logged just 67 mpg—against the 42 mpg they recorded in a stock Prius. ‘At almost $11,000,’ the magazine noted, ‘the plug-in conversion clearly won’t save consumers money overall’—though they deigned to declare the plug-in technology ‘viable.’
The lengthy payback period is one of a handful of criticisms emerging against plug-ins, even as the 2010 production launches of the Chevrolet Volt and Toyota Prius Plug-In draw closer. While the lithium ion batteries used in that Hymotion kit hold the most energy for their size and weight, they’re also the most expensive.
Not all of the dozen or more plug-in converters use lithium cells. A conversion by 3Prong Power in Berkeley, California, for instance, uses old-fashioned lead-acid cells. They weigh more, and give an electric range of only 10 miles, but at a price of $6,700, that may be enough for local users who can recharge between short trips. As research now underway at Carnegie-Mellon University points out, correctly sizing a plug-in battery (which directly affects its cost) depends greatly on how the car will be used.”
