Elon Musk, the chief executive of Tesla, said his company would benefit from what he called “a weak Moore’s Law,” referring to the 8 percent annual improvements in the price performance of lithium-ion batteries. But 8 percent, compounded, would bring too few benefits, too late to Tesla: it would take nine years to halve the price of its battery pack.

The company would not be saddled with such costly components had it not elected to pursue a design that endows its car with both high performance and a long range between charges  244 miles, Tesla says. Earlier this month at the Los Angeles auto show, BMW unveiled its all-electric Mini E, with a smaller battery, a motor with about 20 percent less horsepower than Tesla’s and a shorter range, 150 miles. BMW believes that current technologies used in the all-electric vehicles have not been tested enough in real conditions to be ready to be sold to the public. It will begin by leasing for one year a fleet of 500 Mini E’s for $850 a month each. At the end of the lease term, the cars will be returned to BMW for testing.

Tesla would have needed a much smaller battery pack had it forsaken the all-electric design and instead offered a plug-in hybrid, a more affordable design that many auto manufacturers are readying for production, like that for the Chevrolet Volt. An electric motor provides the primary motive force, and a small internal combustion engine serves as an auxiliary source of power to extend the range that the car can go between charges. The battery need be no bigger than what is necessary to provide enough juice to go 40 miles, the maximum daily round-trip commuting distance for 78 percent of surveyed households, according to a widely quoted Department of Transportation study in 2003.

Tesla pitches all-electric cars as the greenest form of personal transportation, eliminating vehicle emissions and helping to wean the United States from its dependence on foreign oil. The cars reduce air pollution indirectly, to whatever degree the power generation on the grid uses energy sources other than coal. And for households that install their own power-generating solar panels, electric cars can rightfully claim to attain truly zero emissions today.

LAST week, I visited the Tesla showroom in Menlo Park, Calif., and took the Roadster out on the highway. As I headed back to the showroom and waited at red lights, ready to hit the accelerator and fly, I realized that I was experiencing a guilty pleasure derived not just from the speed available at my touch but also from temporarily possessing something that shouted to the world its exclusiveness.

Tesla says it is assembling about 15 cars a week and has delivered only about 80 to date. Many of those have gone to the Valley’s billionaires and centimillionaires who are Tesla investors as well as early customers; these include Sergey Brin and Larry Page, the co-founders of Google, and Jeff Skoll, co-founder of eBay. The company’s principal financier is Mr. Musk, who attained considerable wealth as a co-founder of PayPal.