A method for controlling a portable power system, comprising: using a processor, selecting an engine efficiency range for a engine of a generator set of the portable power system, the engine efficiency range corresponding to a power output range of the generator set and to a power demand of a load coupled to the portable power system; when the power demand of the load is less than the power output of the generator set, storing excess power from the generator set in a first battery bank of the portable power system; when the power demand of the load is greater than the power output of the generator set, providing additional power to the load from a second battery bank of the portable power system; and, when at least one of a predetermined depth of discharge threshold is reached by the second battery bank and a predetermined state of charge threshold is reached by the first battery bank, switching between the second battery bank and the first battery bank.