In this paper, efficient approximate solutions are developed for microscale diffusion inside porous electrodes. Approximate solutions developed for the microscale diffusion are then coupled with governing equations for the macroscale to predict the electrochemical behavior of a lithium-ion cell sandwich. Approximate solutions developed facilitate the numerical simulation of batteries by reducing the number of differential algebraic equations resulting from the discretization of governing equations. (c) 2005 The Electrochemical Society.