Different reasons are suspected for causing the two highly publicised battery malfunctions that led to the worldwide ground of the Boeing 787 fleet.
The US National Transportation Safety Board (NTSB) says the battery that starts the auxiliary power unit (APU) was not over-charged when it spread smoke and flames inside a small compartment of a parked Japan Airlines 787 in Boston on 7 January.
That NTSB finding came about 24h after the Japan Transportation Safety Board suggested the 32V lithium-ion main battery on an All Nippon Airways 787 was over-charged on 15 January, forcing the flight crew to make an emergency landing in Japan.
The differences appear to complicate the solution to the battery problem, perhaps suggesting a separate fix may be necessary to prevent such malfunctions in the future.
In a move copied by civil aviation authorities globally, the Federal Aviation Administration on 16 January grounded the 787 indefinitely until the batteries are demonstrated to be safe.
Although the two battery incidents since 7 January were cited by the FAA, ANA has said that it has replaced several other malfunctioning batteries since introducing the 787 into service in October 2011.
The NTSB also provided details of its ongoing investigation of the JAL 787 main battery. It has completed X-Ray and computed tomography (CT) scans at the NSTB Materials Laboratory in Washington DC. The eight cells inside the APU battery have been disassembled.
Other components have been sent to Boeing's testing facility in Seattle and battery supplier GS Yuasa's headquarters in Japan, while the NTSB is is testing the Hamilton Sundstrand-built APU controller, the Securaplane-designed battery charger and the start power unit.