A transport refrigeration unit for controllably cooling a container, the transport refrigeration unit comprising: a compressor constructed and arranged to compress a refrigerant; a compressor motor configured to drive the compressor; a condenser heat exchanger operatively coupled to the compressor; a condenser fan configured to provide air flow over the condenser heat exchanger; a condenser fan motor for driving the condenser fan; an evaporator heat exchanger operatively coupled to the compressor; an evaporator fan configured to provide air flow over the evaporator heat exchanger; an evaporator fan motor for driving the evaporator fan; a battery configured to at least in-part provide electric power to the compressor motor; a battery charger configured to charge the battery; a generator configured to provide electric power to the compressor motor and the battery charger; a combustion engine constructed and arranged to drive the generator; and a power management system including a battery temperature sensor, a battery current sensor, a compressor motor current sensor, a generator current sensor and a computer-based controller configured to receive and process respective signals from the battery temperature sensor, the battery current sensor, the compressor motor current sensor and the generator current sensor for generating diagnostic data; wherein the power management system is configured to control power distribution via the generator and/or the battery; wherein the battery charger is powered by the generator during part-load operating conditions of the transport refrigeration unit; wherein at least one of the generator and the battery is configured to provide electric power to the condenser fan and evaporator fan motors; wherein the power management system includes an engine coolant temperature sensor configured to output a signal to the computer-based controller toward generation of the diagnostic data; and wherein the power management system includes an engine speed sensor configured to output a signal to the computer-based controller toward generation of the diagnostic data. a compressor constructed and arranged to compress a refrigerant; a compressor motor configured to drive the compressor; a condenser heat exchanger operatively coupled to the compressor; a condenser fan configured to provide air flow over the condenser heat exchanger; a condenser fan motor for driving the condenser fan; an evaporator heat exchanger operatively coupled to the compressor; an evaporator fan configured to provide air flow over the evaporator heat exchanger; an evaporator fan motor for driving the evaporator fan; a battery configured to at least in-part provide electric power to the compressor motor; a battery charger configured to charge the battery; a generator configured to provide electric power to the compressor motor and the battery charger; a combustion engine constructed and arranged to drive the generator; and a power management system including a battery temperature sensor, a battery current sensor, a compressor motor current sensor, a generator current sensor and a computer-based controller configured to receive and process respective signals from the battery temperature sensor, the battery current sensor, the compressor motor current sensor and the generator current sensor for generating diagnostic data; wherein the power management system is configured to control power distribution via the generator and/or the battery; wherein the battery charger is powered by the generator during part-load operating conditions of the transport refrigeration unit; wherein at least one of the generator and the battery is configured to provide electric power to the condenser fan and evaporator fan motors; wherein the power management system includes an engine coolant temperature sensor configured to output a signal to the computer-based controller toward generation of the diagnostic data; and wherein the power management system includes an engine speed sensor configured to output a signal to the computer-based controller toward generation of the diagnostic data.