The voltage drop was consistent with the charge of a single cell on the eight-cell battery, she said.

CNN: Boeing can conduct Dreamliner test flights

Analysis of a flight recorder from that plane showed that a lithium-ion battery experienced a sudden drop in voltage and was not overcharged, the Japan Transport Safety Board said Wednesday.

CNN: What's wrong with the Dreamliner?

Speaking about the January 7 fire in Boston, Hersman said the plane's flight data recorder showed the battery underwent an unexplained drop in voltage from 32 volts to 28 immediately before the incident, as the plane was being serviced on the tarmac.

CNN: Boeing can conduct Dreamliner test flights