Disclosed is a method for an electronic control unit to prevent the discharge of a battery. The method includes the steps of detecting an off signal of vehicle function power connected to a battery and monitoring a voltage of the battery, detecting a low voltage of the battery based on a result of the monitoring and transmitting an operation inhibition signal for preventing power consumption of the battery to a plurality of controllers, and determining whether the plurality of controllers switch to a sleep mode in response to the operation inhibition signal.