NOVELTY - The system has an auxiliary power unit (26) supplying charge to a battery. A system controller (28) monitors a parameter of a machine, automatically starts the power unit when the parameter is outside a preset range, and brings the parameter within another preset range using the power unit. A cooling system (20) circulates coolant via a main engine and the power unit, where the circulation of the coolant e.g. water, is occurred via the used coolant reservoirs. The power unit warms coolant of the cooling system of the machine, where the parameter is indicative of a temperature of the coolant.    USE - Used for assisting a main engine start of a work machine (claimed) e.g. on and off highway vehicle such as truck, boat, recreational vehicle and passenger car, industrial/construction equipment and generator set, and also for a device e.g. radio, television, refrigerator, and heating and cooling device.    ADVANTAGE - The controller monitors the parameter of the machine, automatically starts the auxiliary power unit when the parameter is outside one preset range, and brings the parameter within another preset range using the power unit, thus assuring that the battery voltage necessary for the main engine start is maintained, and ensuring that the main engine starts only upon a request, and hence avoiding an expensive and time consuming jump-start or tow to a repair facility. The system also contributes longer life cycles for work machine components, and reduces frequent maintenance/repair of the machine. The system enables a machine owner to reduce battery maintenance intervals, and extend battery life, thus improving operating costs of the machine and reducing the probability of starter solenoid damage due to low voltage during starting, and hence increasing starter life. The auxiliary power unit warms the coolant, thus enabling easy main engine turn over, and hence reducing wear on starting components in extreme weather conditions.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) a method for automatically starting an auxiliary power unit    (2) a work machine comprising a main engine.    DESCRIPTION OF DRAWING(S) - The drawing shows a block representation of an auxiliary power unit automatic start-up system.    Cooling system (20)    Electrical connection (23, 25)    Power electronic module (24)    Auxiliary power unit (APU) (26)