A method of managing electric power flow in a vehicle powertrain includes recording operator input indicative of a current request for electric power. An amount of the currently requested electric power corresponding with the recorded operator input is determined. This amount is averaged with amounts of requested electric power based on previously recorded operator input recorded over time. An amount of electric power required from an auxiliary power unit to satisfy the current request for electric power is determined based at least in part on the averaged requested electric power for propulsion. A powertrain has an electric motor/generator, a battery operable to provide electric power to the electric motor/generator, and an auxiliary power unit operable to supplement the battery. The auxiliary power unit includes an engine and a generator. A processor with a stored algorithm carries out the method.