A battery heating system, comprising: a battery group having a positive pole and a negative pole; a switch having a first end connected with the positive pole; a large-current discharge module, a first end of the large-current discharge module being connected to a second end of the switch, and a second end of the large-current discharge module being connected to the negative pole; a controller connected to the switch and configured to control the switch according to a temperature of the battery group; a PTC heating module disposed on a surface of the battery group and connected to the switch, wherein the large-current discharge module has a discharge current of 400A to 500A, and when the switch is turned on, the battery group discharges via the large-current discharge module and is heated due to an internal resistance thereof, and the PTC heating module heats the battery group from an outside of the battery group; an adjustable resistor connected to the large-current discharge module in series, and a current detecting module configured to detect a heating current of the battery group; wherein the controller is further configured to adjust a resistance of the adjustable resistor so as to adjust the heating current of the battery group; and a sealed container, and cooling liquid received in the sealed container, wherein the large-current discharge module and the adjustable resistor are dipped in the cooling liquid, and the cooling liquid is configured to cool the large-current discharge module and the adjustable resistor, wherein the sealed container is made preferably of non-conducting material. a battery group having a positive pole and a negative pole; a switch having a first end connected with the positive pole; a large-current discharge module, a first end of the large-current discharge module being connected to a second end of the switch, and a second end of the large-current discharge module being connected to the negative pole; a controller connected to the switch and configured to control the switch according to a temperature of the battery group; a PTC heating module disposed on a surface of the battery group and connected to the switch, wherein the large-current discharge module has a discharge current of 400A to 500A, and when the switch is turned on, the battery group discharges via the large-current discharge module and is heated due to an internal resistance thereof, and the PTC heating module heats the battery group from an outside of the battery group; an adjustable resistor connected to the large-current discharge module in series, and a current detecting module configured to detect a heating current of the battery group; wherein the controller is further configured to adjust a resistance of the adjustable resistor so as to adjust the heating current of the battery group; and a sealed container, and cooling liquid received in the sealed container, wherein the large-current discharge module and the adjustable resistor are dipped in the cooling liquid, and the cooling liquid is configured to cool the large-current discharge module and the adjustable resistor, wherein the sealed container is made preferably of non-conducting material.