Embodiments of the present disclosure provide a battery heating system, a battery assembly and an electric vehicle. The battery heating system includes: a battery group having a positive terminal and a negative terminal; a switch having a first end connected with the positive terminal; a large-current discharge module, and a controller connected to the switch and configured to control the switch according to a temperature of the battery group. A first end of the large-current discharge module is connected to a second end of the switch, and a second end of the large-current discharge module is connected to the negative terminal. When the switch is turned on, the battery group discharges via the large-current discharge module and the battery group is heated due to an internal resistance thereof.