Abstract: Control apparatus is provided for a medical diagnostic imaging system, such as a mobile X-ray unit. The imaging system includes a battery or like power storage device of limited capacity, and a number of components disposed to perform respective corresponding functions. The control apparatus includes a user interface for enabling an operator to generate commands which selectively direct the components to perform their respective corresponding functions. The control apparatus further includes a system control means, comprising a controller and set of control circuits, for initially placing the imaging system in a powered-up mode, wherein each component is coupled to receive power from the battery. A sleep mode activation device is included in the system control for decoupling a first set of components from the battery, while allowing a second set of components to remain coupled thereto, following a first time period during which no command is generated by the user interface.