A hybrid battery system for an electric vehicle, comprising: a lithium battery module including a plurality of lithium battery cells; a lead storage battery module including a plurality of lead storage battery cells; a first sensing unit including a sensor for measuring a temperature and a voltage of the lithium battery module; a second sensing unit including a sensor for measuring a temperature and a voltage of the lead storage battery module; a control circuit connected to the first sensing unit and the second sensing unit, the control circuit configured to measure a state of charge of each of the lithium battery module and the lead storage battery module by using the temperature and the voltage measured in the first sensing unit and the second sensing unit and to generate a control signal by comparing the temperature of the lithium battery module with a reference temperature and comparing the voltage of the lead storage battery module with a reference voltage; and a charging/discharging circuit connected to the lithium battery module and the lead storage battery module, the hybrid battery system being characterized by charging/discharging circuit including a switch for selectively discharging the lithium battery module or the lead storage battery module in response to the control signal, wherein the control circuit is configured to generate a control signal for discharging the lead storage battery module, if the temperature of the lithium battery module is equal to or higher than the reference temperature and if the voltage of the lead storage battery module is equal to or higher than the reference voltage, and to generate a control signal for discharging the lithium battery module, if the temperature of the lithium battery module is lower than the reference temperature and if the voltage of the lead storage battery module is lower than the reference voltage. a lithium battery module including a plurality of lithium battery cells; a lead storage battery module including a plurality of lead storage battery cells; a first sensing unit including a sensor for measuring a temperature and a voltage of the lithium battery module; a second sensing unit including a sensor for measuring a temperature and a voltage of the lead storage battery module; a control circuit connected to the first sensing unit and the second sensing unit, the control circuit configured to measure a state of charge of each of the lithium battery module and the lead storage battery module by using the temperature and the voltage measured in the first sensing unit and the second sensing unit and to generate a control signal by comparing the temperature of the lithium battery module with a reference temperature and comparing the voltage of the lead storage battery module with a reference voltage; and a charging/discharging circuit connected to the lithium battery module and the lead storage battery module, the hybrid battery system being characterized by charging/discharging circuit including a switch for selectively discharging the lithium battery module or the lead storage battery module in response to the control signal, wherein the control circuit is configured to generate a control signal for discharging the lead storage battery module, if the temperature of the lithium battery module is equal to or higher than the reference temperature and if the voltage of the lead storage battery module is equal to or higher than the reference voltage, and to generate a control signal for discharging the lithium battery module, if the temperature of the lithium battery module is lower than the reference temperature and if the voltage of the lead storage battery module is lower than the reference voltage.