Abstract: An auxiliary energy management system includes a power assist device connected to a turbocharger of a mobile power plant and operable in either electric motor or alternator modes to supply or receive rotary drive motion to or from the turbocharger, an energy storage device connected between the assist device and a main alternator of the plant and operable in either energy capture or supply modes to store electrical power or provide it to auxiliary power loads, and a control mechanism connected to the assist and storage devices and operable to convert the assist device between motor and alternator modes in response to sensing performance of the turbocharger and a diesel engine of the plant and operate the storage device in supply or capture modes.