The National Transportation Safety Board said in a statement that its investigators plan to disassemble the battery this week after studying the internal condition of the battery via X-rays at an independent test facility over the weekend.

Investigators also took possession of burned wire bundles, the auxiliary power unit APU.L battery charger and several memory modules to search for any available data.

The airplane's two combined flight data recorder and cockpit voice recorder units were also brought to NTSB headquarters and are being analyzed by the investigative team.

The fire occurred aboard one of Boeing Co's (BA.N) sophisticated new 787 Dreamliner jets on January 7 at Logan Airport. A mechanic inspecting the Japan Airlines Co Ltd (9201.T) jet discovered smoke in the cockpit while performing a routine post-flight inspection on January 7. There were no passengers on board.

The NTSB said fire and rescue personnel reported having difficulty accessing the battery for removal when they were trying to extinguish the fire.

After releasing the statement, the NTSB sent out a tweet saying it had released the airplane involved in the battery fire back to Japan Airlines.

The investigation includes representatives named by the Japan Transport Safety Board and French civil aviation security authorities. Others included in the NTSB-led team are experts from the Federal Aviation Administration, Boeing, U.S. Naval Surface Warfare Center's Carderock Division, Japan Airlines, battery manufacturer GS Yuasa (6674.T) and APU battery/charger system provider Thales Avionics Electrical Systems.

(Reporting by Deborah Charles; Editing by Gary Hill, Leslie Adler and Tim Dobbyn)

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