The American prices amount to roughly half of the price of comparable batteries in Germany, depending on how the battery is used, according to Michael Sterner, a professor of energy storage at the Technical University of Regensburg. However, he noted that the price does not include an inverter. (In a partnership, Fronius is set to distribute an inverter to accompany Tesla’s battery in Europe, and Fronius will also continue to sell its own battery.)

Germany is a particularly promising market for battery makers like Tesla. Homeowners have a powerful incentive to store solar-generated electricity and use it for their homes, rather than sell it to the local grid — but only if batteries are cheap enough. That’s because homeowners there pay much higher prices to buy grid electricity than they can receive for selling the excess power, said Sam Wilkinson, a research manager for energy storage at IHS Technology, a global research company. Tesla’s low prices will make it more economical for German households to keep their own battery, said Mr. Wilkinson. Currently, solar power alone makes more economic sense than solar systems with a battery, but this will change as battery prices fall, he said.

But Tesla cannot take the German market for granted, Dr. Sterner said.

“Tesla has first to prove that they can stay in the market at that price,” and also prove that its products are durable, he said.

Other companies are ramping up production of their own battery packs. For example, Kyocera Corporation, a Japanese electronics manufacturer, sells home energy-storage systems in Japan and Germany using Samsung lithium-ion batteries. The company plans to unveil a larger battery system, capable of storing 12 kilowatt-hours of energy, in Japan next month.

Economics aside, other hurdles still stand in the way of home batteries. Electric utilities, Dr. Sterner said, may not welcome the idea of former customers becoming more self-sufficient.

“As you plant your own tree to get your own apple, the apple industry will make losses,” he said.

Battery testers in Germany also fear the public-relations consequences if a low-quality battery catches on fire, he said. If a home burns down, people could avoid buying batteries. (Electric car batteries catching fire have jolted Tesla’s share price in the past, an issue that the company has addressed by adding an underbody shield.)

Those who have already installed batteries seem undaunted by the challenges of a new technology. Kelly Taylor-Faye, a resident of a small village in the central Canadian province of Saskatchewan, decided to go off the grid, partly because connecting to a utility power line would have cost about 15,500 Canadian dollars, or $12,900, at the time in 2009. So he and his wife added a type of lead-acid battery commonly used in the mining industry to store energy generated by their wind turbine and solar panels.