A system and methods for controlling an electric motor in an electric vehicle. The system includes a battery management system and a motor controller. The battery management system monitors output voltage of each individual cell unit in a battery pack with a plurality of cell units and generates a state signal and a count value according to the monitored output voltages. The motor controller receives the state signal and the count value from the battery management system and controls the output current to the electrical motor. The battery management system generates the state signal in a first state if none of the monitored output voltages is below a predefined voltage for longer than a predefined period. The battery management system increases the count value each time a monitored output voltage drops below the predefined voltage. The cell units in the battery pack are protected by the battery management system.