The modeling of Li-ion batteries may work as a powerful tool for the introduction and widespread testing of this technology in alternative energy storage, hybrid, and electric vehicle applications. In this paper, the authors propose a model for Li-ion batteries that is based on a typical equivalent electrical circuit (EEC) representation of these batteries and valid over a wide frequency range (2 mHz-65 kHz). However, a full parameterization of EEC models was not possible only with the electrochemical impedance spectroscopy (EIS) method, particularly at high charge/discharge currents. Therefore, a method combining EIS and charge/discharge curves analysis has been developed. The simulated and experimental results were compared, and it was demonstrated that the developed method provides accurate predictions of the dynamic behavior of Li-ion batteries over wide state of charge and charge/discharge current range. (C) 2011 The Electrochemical Society. [DOI:10.1149/1.3543710] All rights reserved.