United Technologies, which builds the aircraft's auxiliary power unit, said it would also cooperate.

BBC: Dreamliner: Japan and US probe battery maker

Officials found that the battery for the aircraft's auxiliary power unit was incorrectly connected to the main battery that overheated.

BBC: Boeing 'set to offer plan to fix Dreamliner battery'

The ES is critical to aircraft operation it distributes power around the aircraft from the engines and the Auxiliary Power Unit (APU) which provides the power to operate the air conditioning and to start the engines at the gate to all the systems requiring electricity.

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