The batteries are made by GS Yuasa of Japan. Japanese aviation investigators probing the cause of the ANA battery failure have also found there was thermal runaway.
Investigators have ruled out mechanical damage or external short-circuiting as possible causes of the initial, internal battery short-circuiting, Hersman said. Investigators and technical experts are now looking for evidence of flaws inside the batteries like pinches, wrinkles or folds, she said.
"We are looking at a number of scenarios," Hersman said, including the state of charge of the battery, its manufacturing processes and the design of the batteries.
"We haven't reached any conclusions at this point," she said. "We really have a lot of work to do."
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Freed contributed from Minneapolis.
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