A range of things can cause the light to come on, some are problem driven some are rogue and some are as you suggest low battery voltage etc. There is no external reset procedure on the Ford system in so much as buttons to press etc, the code has to be read and then cleared using an external code reader plugged into what's known as the OBD2 socket. You have not said where you are? If your near Leicester I have one and happy too do it for you or visit your local Ford dealer and ask them for a code reset....they often help given interest in the car. The OBD2 socket is a black plug on a lead normally tucked up alongside the glovebox between it and the heater. Not a bad idea to get yourself a Ford compatable code reader for a Duratec engined Focus/Mondeo.....you can get decent ones for around £20-30
