Earlier this week, Senator John McCain, the presumptive Republican presidential nominee, proposed a $300 million federally funded prize to spur the development of a vastly improved battery for electric cars and plug-in hybrids. While McCain offered few specifics, industry experts say that in targeting battery costs, he has identified a major obstacle to reducing fuel consumption in cars.

“Current vehicle-battery developers all recognize that reducing battery cost is instrumental in the adoption of hybrid-electric and plug-in hybrid vehicles” that recharge from the power grid, says Yet-Ming Chiang, founder of A123 Systems, a Watertown, MA, company that develops advanced lithium-ion batteries and is working with several carmakers on plug-in hybrids. “Offering this prize is a great way to focus attention on the problem and get the dialogue going on how we will solve it. I would love to compete for this prize, and the wheels are turning in my mind.”

McCain said that new batteries should “leapfrog” the size, capacity, and power of commercially available models, and at 30 percent of current costs. But since plug-in hybrids are not on the market yet, there is no clear basis for estimating a cost savings. “It’s hard to measure without a benchmark,” says Gerbrand Ceder, a professor of materials science and engineering at MIT. Ceder calls the McCain statement a “political stunt” and says that the money would be better invested in R&D than in an after-the-fact prize. The McCain campaign did not return a phone call seeking more specifics.

Ceder estimates that it will cost around $5,000 to manufacture a plug-in-hybrid battery that holds 10 kilowatt-hours of electricity. But 10 kilowatt-hours doesn’t get you very far; the Volt, a plug-in hybrid being developed by Chevrolet, lists an electric-drive range of 40 miles on a battery that holds 16 kilowatt-hours of electricity. Cutting battery costs by 70 percent–while further boosting capacity and range in a battery of manageable size–“will require a serious amount of innovation, new materials, and new manufacturing procedures,” Ceder says.

The sum that McCain cited would, however, represent a substantial increase in federal investment in battery technology. In 2008, the U.S. Department of Energy (DOE) devoted nearly $50 million to research and development for vehicle-related energy storage. James Barnes, a program manager for the DOE, says that $300 million would fund ample battery R&D with enough left over to set up an actual manufacturing plant.