An equivalent electrical circuit model based on parameters taken from ac impedance measurements obtained from a Li-ion polymer battery is simulated in a Matlab/Simulink environment. The model representation contains relevant parameters, including ohmic resistance, slow migration of Li-ions through the surface layers, faradaic charge transfer process, solid-state diffusion of Li-ions, and charge accumulation (intercalation capacitance) within the host material. The model also takes into account the non-homogeneous distribution properties (e.g, particle size, pore geometry) of the electrode which account for deviation from the ideal finite space Warburg behavior. The simulated and experimental results are compared and demonstrate that the impedance model can accurately predict the discharge power performance and transient and dynamic behavior of the Li-ion polymer batteries. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.2999375] All rights reserved.