This paper proposed a separated-frequency identification method of Li-ion battery model for Electric Vehicles (EVs). The main idea is to decompose the measured terminal voltage and current data in wavelet domain, and then the weighting least squares (LS) algorithm is used to extract the model parameters. Since the signal energy of open circuit voltage (OCV) mainly distributes in the low frequency band, the identifiable wavelet-domain battery model can be approximately obtained by neglecting the high frequency wavelet decomposition coefficients. Furthermore, based on the Akaike’s information criterion, we study the optimum decomposition order of the wavelet-domain battery model.