Electric vehicles are still too expensive and have too many limitations to compete with regular cars, except in a few niche markets. Will that ever change? The answer has everything to do with battery technology. Batteries carrying more charge for a lower price could extend the range of electric cars from today's 70 miles to hundreds of miles, effectively challenging the internal-combustion motor.

To get there, many experts agree, a major shift in battery technology may be needed. Electric vehicles such as the all-electric Nissan Leaf and the Chevrolet Volt, a plug-in hybrid from GM, rely on larger versions of the lithium-ion batteries that power smart phones, iPads, and ultrathin laptops. Such gadgets are possible only because lithium-ion batteries have twice the energy density of the nickel–metal hydride batteries used in the brick-size mobile phones and other bulky consumer electronics of the 1980s.

Using lithium-ion batteries, companies like Nissan, which has sold 20,000 Leafs globally (the car is priced at $33,000 in the U.S.), are predicting that they've already hit upon the right mix of vehicle range and sticker price to satisfy many commuters who drive limited distances.

The problem, however, is that despite several decades of optimization, lithium-ion batteries are still expensive and limited in performance, and they will probably not get much better. Assembled battery packs for a vehicle like the Volt cost roughly $10,000 and deliver about 40 miles before an internal-combustion engine kicks in to extend the charge. The battery for the Leaf costs about $15,000 (according to estimates from the Department of Energy) and delivers about 70 miles of driving, depending on various conditions. According to an analysis by the National Academy of Sciences, plug-in hybrid electric vehicles with a 40-mile electric range are "unlikely" to be cost competitive with conventional cars before 2040, assuming gasoline prices of $4 per gallon.

Estimates of the cost of assembled lithium-ion battery packs vary widely (see "Will Electric Vehicles Finally Succeed?"). The NAS report put the cost at about $625 to $850 per kilowatt-hour of energy; a Volt-like car requires a battery capacity of 16 kilowatts. But the bottom line is that batteries need to get far cheaper and provide far greater range if electric vehicles are ever to become truly popular.