The driver squeezes down on the accelerator pedal, and the little roadster responds like a racehorse at the starting gate, launching aggressively down the pavement.

Twenty, forty, sixty, we've gone extra-legal in little more than a heartbeat, and yet something is wrong. Something is missing, and it's precisely the heartbeat, the resonant roar you expect of a high-performance sports car pushed to the edge. But with the little Tesla roadster, all we hear is the wind in our hair, tires slapping pavement, and a surprisingly gentle whine.

Then again, that's really no surprise, because instead of a traditional internal combustion engine, Tesla's two-seat offering is driven by a slick 250-horsepower electric motor. Weighing in at a mere 77 pounds, the motor is powerful enough to help launch the electric Roadster from 0-60, company officials claim, in barely five seconds.

That's if the Tesla Roadster actually ever makes it into production, something many skeptics are questioning. But despite a series of delays, work goes on at a hectic pace in the suburban San Francisco complex that is home to the potentially revolutionary start-up company.

"We're getting there," insists Dave Vespremi, the young and enthusiastic executive who does double-duty - like many Tesla officials - as public relations chief.

The electric warehouse

After months of calls and e-mails, Vespremi has finally agreed to let us visit the nondescript San Carlos warehouse that's serving as Tesla's development center.  Inside, a visitor passes first the full-size clay model that stood in during aerodynamic testing, as well as an assortment of running prototypes, some newer, some older. The latest, dubbed VP10, a verification prototype we'll get to drive, reveal the changes - both subtle and substantial - that the roadster has been undergoing in its drive to market.

The fundamentals are largely the same as they were when the high-tech start-up made its debut, several years ago, promising to show how electric power could not only be green, but lots of fun. Unlike a conventional automobile, the heart of Tesla's beast is its battery pack, which actually consists of 6831 individual computer-style lithium-ion cells, each about the size of a prescription pill bottle.

According to Vespremi, a disproportionate share of engineering work, and "the lion's share" of the cost of the project has gone into developing a sustainable battery pack. While lithium-ion technology today powers plenty of consumer electronic devices, from cellphones to laptop computers, it's another thing entirely to drive an automobile, a high-performance one, at that.

To survive the tough automotive environment, Tesla had to devise a slick climate control system, maintaining steady room temperatures and low humidity in everything from snow to sandstorms. And considering lithium-ion's volatile nature, a sophisticated interconnection system was developed to prevent the failure of one cell from crashing the other 6830.

While performance and mileage numbers - over 200 miles per charge - have been gaining most of the public's attention, what is perhaps even more significant is Tesla's decision to warrant the car, and especially the batteries, for a full 100,000 miles of driving.

A web of wires links the pack to the Taiwanese-made motor. The size of a watermelon, it can rev to 13,000 rpm.

"It's got the low-end torque of a truck," explains Vespremi, "and the top end of a super-bike."

Mounted amidship, it's mated to a two-speed, clutchless transmission that can hit 65 mph in first. There's no reverse. The electronics just change the polarity of the motor, which drives the rear wheels.