A method for detecting a state of charge (SOC) of a battery is disclosed. The method includes inputting a pulse to the battery for receiving a response curve of the battery associated with the pulse inputted to the battery, determining a set of parameters for preparing a simulated curve, comparing a difference between the response curve and the simulated curve, determining whether the difference between the simulated curve and the response curve is less than a predetermined threshold before further utilizing the parameters to determine the SOC from a corresponding relationship.