The push to get electric cars on the road is backed by governments and auto makers around the world, but they face a big hurdle: the stubbornly high cost of the giant battery packs, which can account for half the cost of an electric vehicle.

Both the industry and government are betting that a quick takeoff in electric-car sales will drive down the battery prices. But a number of scientists and automotive engineers believe cost reductions will be hard to come by.

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