Monday, February 7, 2011

Electric-car batteries spur curiosity, questions

SAN JOSE, Calif. — A variety of electric vehicles will hit the market this year, raising questions about the most critical element of any electric car: the battery. How often do you have to replace the battery? Will it be recycled? Can you charge a battery even if it is not empty? How many charging cycles can the battery handle?

Lithium-ion batteries can be found in all kinds of consumer products, from laptops to cell phones, and they also will be the power source in at least the first generation of electric cars. An electric-vehicle battery is basically just a cluster of thousands of cell phone batteries packaged together.
"If I want to buy an electric vehicle, I would want to know how many miles can I drive under real driving conditions, how long will my battery last and how long will the battery take to charge," said Venkat Srinivasan, a staff scientist at the Lawrence Berkeley National Laboratory in California who writes a popular battery blog at

The Chevrolet Volt and Nissan Leaf, the first mainstream plug-ins to reach the market, both offer battery warranties good for 100,000 miles or eight years. That will reassure many consumers, but there still are things they can do to maximize battery life and performance.

"Don't keep continuously fully charging and discharging them," Srinivasan said. "Pressing on the accelerator too much also draws power from the battery at a high rate, and can cause degradation."

Keep it cool

Sunil M. Chhaya, an electric drive expert at the Electric Power Research Institute, notes that batteries age faster if the temperature of the battery is frequently elevated. The institute's research has found that heat management inside the batteries is the single most important predictor of battery health and longevity. That's one reason why Tesla uses a liquid cooling system to maximize the life of its battery packs.

"Batteries are like people and perform nicely when their operating temperature is in a 20-45 degrees Celsius (or 68-113 degrees Fahrenheit) window," Chhaya said. "Outside of it, they need to be 'thermally managed.' "

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