The computer system responds to a first trigger event to enter a partial off state in which a boot cycle is required to return to a working state. A device plugged into a serial bus port can be charged in the partial off state. A configuration register or runtime environment controls whether the computer system enters the partial off state in response to a trigger event. The computer system stays in the partial off state until another trigger event returns the computer system to the working state. In some implementations, the computer system leaves the partial off state and enters the shutdown state after an unplug event, a predetermined amount of time after an unplug event, a predetermined amount of time after entering the partial off state, a predetermined amount of time after charging of a device is complete, or any combination of such events.