An auxiliary power unit (APU) is used to charge the first battery to maintain a desired voltage across the first energy storage unit.

以及辅助动力单元，其可操作以给所述第一能量存储单元充电。

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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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