Abstract: A system identification method executed by a system identification device that estimates a response of a system having a current flowing in a battery as input and an overvoltage of the battery as output, comprises: a first step of identifying the system by applying a model of the battery including a FIR model and an ARX model to the system, based on time series data of each of the current flowing in the battery and the overvoltage of the battery in a predetermined period; and a second step of estimating, based on the model of the battery, the overvoltage of the battery output from the system at an estimation target time after an input start time in the case where no current is input before the input start time and the current is input to the system from the input start time onwards.