I came across an interesting article on Fox News

Experimental Hybrid Cars Get Up to 250 Mpg

It looks like a typical Toyota Prius hybrid (search), but in the trunk sits an 80-miles-per-gallon secret — a stack of 18 brick-sized batteries that boosts the car’s high mileage with an extra electrical charge so it can burn even less fuel.

Gremban, an electrical engineer and committed environmentalist, spent several months and $3,000 tinkering with his car.

Like all hybrids, his Prius increases fuel efficiency (search) by harnessing small amounts of electricity generated during braking and coasting. The extra batteries let him store extra power by plugging the car into a wall outlet at his home in this San Francisco suburb — all for about a quarter.

He’s part of a small but growing movement. “Plug-in” hybrids aren’t yet cost-efficient, but some of the dozen known experimental models have gotten up to 250 mpg.

…

University of California, Davis engineering professor Andy Frank built a plug-in hybrid from the ground up in 1972 and has since built seven others, one of which gets up to 250 mpg. They were converted from non-hybrids, including a Ford Taurus and Chevrolet Suburban.

Frank has spent $150,000 to $250,000 in research costs on each car, but believes automakers could mass-produce them by adding just $6,000 to each vehicle’s price tag.

Instead, Frank said, automakers promise hydrogen-powered vehicles hailed by President Bush and Gov. Arnold Schwarzenegger, even though hydrogen’s backers acknowledge the cars won’t be widely available for years and would require a vast infrastructure of new fueling stations.

“They’d rather work on something that won’t be in their lifetime, and that’s this hydrogen economy stuff,” Frank said. “They pick this kind of target to get the public off their back, essentially.”

Curiously missing from this article is any mention of a break-even point. Namely that at some price per gallon a $3,000 add-on is well worth the expense. Granted, it comes on top of an already high hybrid price, but a back of the envelop calculation would be welcome.

It sounds very intresting, though I am a bit dubious about the “quarters worth of electricity” bit. If true, that is just staggering.