With its quirky vintage cars and grease-stained floor, pat's garage looks like a typically hip San Francisco auto repair shop. Until you notice that the street outside is overweighted in Toyota Priuses and inside, against the wall, stands a stack of $10,000 batteries made by A123 Systems. Drop one of these 185-pounders into the spare tire well of the Prius, get garage owner Patrick Cadam and partner Nicholas Rothman to tinker with it overnight, and you've got a hybrid that can be plugged into any outlet for maxing your gas mileage. Rothman, fluent in Japanese and a certified Prius technician, says he's performed more than 100 upgrades and is "addicted" to keeping the car's fuel economy at 99.9mpg, which is as high as its display goes.

Plug-in hybrids use 60% less gasoline than nonhybrid cars. Despite their high sticker price, they've earned powerful fans, including former CIA director James Woolsey, Google founders Sergey Brin and Larry Page, and California's Air Resources Board, which has ordered that 58,333 be produced by 2014 as part of the state's climate change policy. In September GM unveiled its Chevy Volt, capable of driving 40 miles on battery power before the battery needs a recharge from the gasoline engine. The Senate also managed to find a place in the $700 billion bailout for a $7,500 tax credit for plug-ins.

Plug-ins are ready to hit the highway, but are drivers? Their behavior has a huge influence on the performance of the technology under the hood. Rothman can get 99.9mpg, but an average driver will get 80, an aggressive one, 60 and a negligent one, who forgets to plug in the vehicle the night before and then drives like Dale Earnhardt Jr., less than 40. Argonne National Lab found that a bad driver who turns on the air conditioner can squash the plug-in's performance by reducing battery range from 40 miles to 15, which won't get most commuters to work and back.

UC, Davis anthropologist Thomas Turrentine and engineer Kenneth Kurani have spent 19 years looking at how the wiring in drivers' heads interfaces with the engineering under the hoods of alternative vehicles. Their interviews with drivers have flipped conventional thinking on its head more than once. While everyone knows how much they pay at the pump, none of 57 households surveyed kept track of annual gas spending. None of the Prius buyers they talked to had ever looked under the hood. One engineer told them he'd done an elaborate spreadsheet of costs for different vehicles but ultimately bought a Ford Escape Hybrid, the car that made the least financial sense, because he wanted to let Detroit know what kind of cars he wants them to build.

Plug-ins may be an entirely different story from hybrids like the Prius. They offer far higher efficiency, but no one knows how to use them or make the most of them. "There's a big behavior variable with the benefits," says Turrentine. To measure that variable, he and Kurani got a two-year, $1.8 million grant this summer from California to upgrade ten Priuses at Pat's Garage and place them in 80 commuter households. The cars will record every plugging-in, every trip, speeds and fuel use. Some dashboards will have screens offering drivers extra feedback to increase their gas mileage. Afterward the profs will interview drivers.

The only thing the researchers can conclude at this stage is that, despite knowing very little about plug-ins, the public is bonkers about them. Hundreds of families volunteered for the study. They sent résumés and photos of their solar panels. One engineer offered up data he'd been gathering on his own driving for two years. There was even an awkward moment during a meeting when a state official asked to be part of the study.

UC, Davis Ph.D. candidate Jonn Axsen designed an online game last year to measure how 2,373 new car-buying households would weigh tradeoffs between cost and fuel efficiency. He found that while nearly 62% of those surveyed wanted a car with gas mileage near 125mpg, only 12% were comfortable with leaving gas behind altogether with an all-electric vehicle, probably out of fear of running out of juice. This emotional trigger could fade as more drivers experience plug-ins. "It's unavoidable that the world will change while we're doing this research," says Kurani.

Google is seeking early answers, too, and doing so through its forte: social engineering. This is a company that decorates the inside of its bathroom stalls with productivity tips. (Example: how to increase type size in a Java program.) The company has a fleet of six Prius plug-ins, averaging 94mpg, and two Ford Escape plug-ins averaging 49mpg, all from Pat's Garage. Even though all the stats are up for public inspection at rechargeit.org, there is no system of shaming for poor mileage. "The more Googley thing to do is to set up a contest for getting the best mileage," says Google engineer Rolf Schreiber. No such contest is planned, but members of the company's climate-change group have an informal rivalry to exceed 105mpg. "I could totally see something erupting in social networks where people compare driving styles," he adds.

Google has bigger plans than improving gas mileage. Like other plug-in champions, Google wants to make hybrids a form of distributed storage, pushing and pulling power to and from the electrical grid to make it more resilient to fluctuations in demand. But simply substituting coal-fired electricity for gasoline is not particularly Googley, hence the giant solar panels that hover like comic-strip thought balloons over its hybrid parking lot. A study by the American Council for an Energy-Efficient Economy suggests that in some states with heavy dependence on coal-fired power, using plug-in hybrids releases as much greenhouse gas as driving unimproved Priuses.

"When you look at the horizon, there are chances for big changes here," says Schreiber. "West Texas wind blows in the middle of the night, when the electricity is almost worthless!" Hybrids plugged in at night could capture that electricity and redirect it to the morning commute or feed it back onto the grid at noon when it's worth something.

Willett Kempton, a professor of marine policy at the University of Delaware, who runs its carbon-free energy program, says owners of plug-ins should be given an incentive to make their batteries available to the grid. Frequency regulation--the minute-by-minute balancing of electrical current on the grid--is already a service worth $40 per megawatt-hour delivered. He estimates that some plug-in drivers could earn $2,000 a year by making their batteries available as reservoirs. Now he's studying databases of driving habits to see if some groups of people would be better candidates than others. "Some people have very erratic and bizarre driving patterns, like volunteer firemen," says Kempton.

For decades Americans have embraced the cognitive dissonance of sitting in traffic during punishing commutes while claiming that what they value about their cars is the sense of independence and the open road. Are we ready to let rationality intrude on our sacred relationship with our cars?