Automakers are wary of the added weight, cost of batteries, but they're willing to listen. Jim Motavalli - New York Times – April 12, 2006 Hymotion Hybrid vehicles like the Ford Escape Hybrid may be able to double their gas mileage once their battery packs are changed and allowed to recharge through a normal electrical outlet. DANBURY, Conn. -- James Landi, engineering manager at Electro Energy, rolled back the trunk carpet in his company's modified Toyota Prius to reveal two accessories you will not find on a production version of the hybrid car: a plug-in battery charger and a larger-than-stock battery pack capable of storing six kilowatt-hours of electricity. You cannot plug in a regular Prius, or any other hybrid on the market. But even six years after hybrids went on sale, the plug-in misconception is common. To confuse consumers even more, here come hybrids that can be plugged in. Developed by small companies like Electro Energy, Hymotion and EDrive Systems, they are usually based on the Prius and exploit that car's ability to run solely on battery power. While a stock Prius can go only a couple of miles on batteries, larger (or auxiliary) battery packs let plug-in versions stretch their range to 20 miles or more. Automakers are wary of the added weight, cost and complexity, but they are willing to listen, because a hybrid that could complete short commutes on its battery charge alone could achieve the equivalent of more than 100 mpg. Electro Energy, a battery company here, developed its Prius prototype in partnership with a nonprofit group, the California Cars Initiative (CalCars.org), founded by a plug-in enthusiast, Felix Kramer. "For us, conversions are a strategy," he said. "They're designed to get people excited about what the engineers can do." Plug-in hybrids are gaining attention from market-building campaigns by the likes of Plug-In Partners, an umbrella organization of utilities, environmental groups and local governments that is pressuring automakers to make such cars. "Plug-in hybrids are totally available and ready to be manufactured," said Jennifer Krill, zero emissions campaign director for the Rainforest Action Network. But automakers are less enthusiastic. "We think plug-in hybrids are an interesting concept, but the batteries aren't ready," said David Hermance, Toyota's executive engineer for advanced technology vehicles. Countering that assertion is Andrew Frank, a mechanical engineering professor at the University of California, Davis, who has built several plug-in hybrid prototypes with his students. He says such a car can travel 60 miles on electric power alone, using a 350-pound lithium-ion battery pack that is currently available and would last, he says, 150,000 miles. Toyota may have built plug-in hybrids on its own, but it is not showing them, nor has it cooperated with companies like Electro Energy that use the Prius as a base. That poses a big problem for engineers who have to get around a sophisticated computer that wants to switch on the car's gas engine. "You're limited to what you can do if you don't have the source code," Hermance of Toyota conceded. "You have to try and trick the computer." Electro Energy's Prius incorporates a charge circuit designed to do just that -- fool the computer into staying in all-electric mode. Unfortunately, in a test drive around Danbury, the circuit refused to engage. A quick pit stop revealed that the pressure switch connector had fallen off, prompting quick remedial action. Back on the road, the all-electric mode engaged but repeatedly failed after a few seconds, and the engineers concluded that it was being defeated by a combination of steep road grades and state-of-charge factors. The team, with this writer at the wheel, managed three or four miles in all-electric mode, but any Prius owner could go half that far by moving slowly and avoiding hills. A plug-in hybrid designed by an auto manufacturer would obviously have many advantages, starting with a properly programmed computer. All the Prius prototypes switch on their gasoline engines at 35 mph.