1. A method for controlling a state of charge of an energy storage system in a vehicle having an engine and a vehicle control system, the energy storage system having a target state of charge that is adjustable from a baseline target state of charge, the method comprising: inputting to the vehicle control system information related to environmental conditions, including information related to a setting of a vehicle environmental control system; inputting to the vehicle control system information related to current traveling conditions for the vehicle; and adjusting the target state of charge from the baseline target state of charge based on at least one of the inputs to the vehicle control system, including reducing the target state of charge from the baseline state of charge when the vehicle environmental control system performs a function that forces the engine to operate.