Without external power source, Internal battery can ensure the time displays normally.

内置后配电池，保证无外接电源时，时间可常运转。

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The new models of artificial hearts are expected to be equipped with an external power source.

预计给人造心脏的新模型配备一个外部能源系统。

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Motion and speed are sensed without mechanical couplings, bearings, linkages or an external power source.

运动和速度感到无机械轴承，联系或外部电源。

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The engineers found a way to kick-start a radio-frequency device wirelessly using an external power source initially, but running the device afterward on the output of power generated by the inner ear.

WSJ: Harnessing Energy From the Body to Power Devices

Or they can transport heat from an external source of power and manipulate it to cool a surface.

FORBES: The Trillion Mile-Per-Gallon Engine