Are Batteries in Electric Cars Safe?

…Yet even as carmakers race to showcase these green vehicles, some experts are raising concerns about their safety. The worst-case scenario: thermal runaway, which can happen when a short circuit inside a battery sparks a chain reaction, causing overheating or a fire. In mobile phones, laptops, and other portable gadgets, thermal runaway can occur in 1 of every 5 million to 10 million cells, says Brian Barnett, a battery expert at technology firm Tiax in Cambridge, Mass. The incidence can be higher for the products of less experienced battery makers, he says. A laptop battery usually has six cells, but electric cars will likely rely on 75 or 80 cells, meaning they would be more susceptible to problems. Another difference: Cars move at high speeds and carry passengers. “It’s not going to happen all that frequently, but the consequences could be catastrophic,” says Barnett.

There’s a big difference in power, too. And defects might not crop up right away. Laptops were on the market for years before the first reports surfaced about overheating products that burst into flames. Sony’s (SNE) recall of millions of computer batteries took place just three years ago.

Business Week