Mobile chest X-ray machines typically use electricity to generate and control the X-rays in order to display images of the inside of the chest on a screen. Electricity is also used to power other parts of the machine, such as electronic control systems, image storage devices, and so on. Therefore, mobile chest X-ray machines need to be plugged in when they are working.
It should be noted, however, that mobile chest X-ray machines are usually equipped with rechargeable batteries in case of emergencies, such as when filming in places where there are no electrical outlets. These batteries can provide a limited supply of power, but still need to be plugged in to provide continuous power support for the mobile chest camera when working continuously for long periods of time.
In summary, mobile chest X-ray machines usually require plugging in to function properly, but are also equipped with rechargeable batteries for backup power.