Improper Wiring Investigated as Possible Cause of Dreamliner Li-ion Problems

A second battery on a Boeing Dreamliner that made an emergency landing due to smoke linked to its main power unit had also expanded. According to a report on NDTV, detailed examination of the auxiliary power unit (APU) battery of the plane revealed that two of its eight cells were misshapen. An initial inspection found the unit to be intact after the All Nippon Airways (ANA) plane made an emergency landing last month. "Details such as how much they bulged remains unknown," said the official from the Japan Transport Safety Board (JTSB).

A probe into the overheating of a Li-ion battery on the second ANA Dreamliner that made an emergency landing found it was improperly wired, according to Japan's Transport Ministry. The Transport Safety Board said in a report that the battery for the aircraft's auxiliary power unit was incorrectly connected to the main battery that overheated, although a protective valve would have prevented power from the auxiliary unit from causing damage.

Flickering of the plane's tail and wing lights after it landed and the fact the main battery was switched off led the investigators to conclude there was an abnormal current traveling from the auxiliary power unit due to improper wiring.

The agency said more analysis was needed to determine what caused the main battery to overheat and emit the smoke that prompted the Jan. 16 emergency landing of the ANA domestic flight and the worldwide grounding of Boeing 787 jets. They said they are consulting Boeing about the issue.