NOVELTY - The power system has battery group connected with battery heater and battery management device. The device controls (S702) battery heater to heat battery group intermittently when temperature of battery group is lower than first heating threshold and residual electric quantity of battery group is larger than parking electric quantity threshold and controls (S703) heater to stop heating battery group according to current throttle depth change rate when group is in running heating mode. A motor controller is connected with motor and electric distribution box and isolation inductor.    USE - Power system of electric vehicle (claimed).    ADVANTAGE - The internal resistor of the battery can be heated so that the battery group can be heated by using a large current discharge of the battery group in the electric vehicle. The electricity for heating is totally supplied by the battery group without any external power supply. A heating management can be performed for the battery group by the battery management device and the battery heater, which can reduce the restriction on the use of the electric vehicle at the low temperature, thus satisfying the requirements of running and charging at the low temperature. The power system heats the battery group directly, so that higher heating efficiency, a lower cost and a better utility can be obtained. A service life of the battery group can be prolonged and a dynamic property of the electric vehicle can be ensured to avoid an over discharging of the battery group.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for heating battery group.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart illustrating the process for heating battery group.    Step for detecting temperature and residual electric quantity of the battery group (S701)    Step for controlling battery heater to heat the battery group intermittently, if the temperature of the battery group is lower than a first heating threshold and the residual electric quantity of the battery group is larger than a parking electric quantity threshold (S702)    Step for controlling battery heater to stop heating battery group according to current throttle depth change rate of the electric vehicle when the battery group is in a running heating mode (S703)    Step for inhibiting battery group from being heated or charged and the electric vehicle is inhibited from being driven if the temperature of the battery group is lower than the first heating threshold and the residual electric quantity of the battery group is lower than the parking electric quantity threshold (S704)