The Japan Transportation Safety Board said that CAT scans and other analysis found damage to all eight cells in the battery that overheated on the All Nippon Airways 787 on Jan. 16, which prompted an emergency landing and probes by both U.S. and Japanese aviation safety regulators.
They also found signs of short-circuiting and "thermal runaway," a chemical reaction in which rising temperature causes progressively hotter temperatures. U.S. investigators found similar evidence in the battery that caught fire last month on a Japan Airlines 787 parked in Boston.
Photos distributed by the Japanese investigators show severe charring of six of the eight cells in the ANA 787's battery and a frayed and broken earthing wire — meant to minimize the risk of electric shock.
All 50 Boeing 787s in operation are grounded as regulators and Boeing investigate the problem. The Japanese probe is focusing on flight data records and on the charger and other electrical systems connected to the damaged battery.
Lithium ion batteries are more susceptible to catching fire when they overheat or to short-circuit than other types of batteries. Boeing built in safeguards to gain safety certification for use of the relatively light and powerful batteries to power various electrical systems on the 787, the world's first airliner made mostly from lightweight composite materials.
Investigators earlier said they found no evidence of quality problems with production of the 787's batteries by Kyoto, Japan-based, GS Yuasa.