This paper studies the charge conservation equation in the modeling of fuel cells. It is often useful to have an approximate closed form solution to describe the electronic potential in the whole solution domain. In our problem, no small term exists and the perturbation method cannot be used for this purpose. This paper proposes a simple analytical approach by using the method of separation of variables and Galerkin technology, and an analytical solution is obtained, which is valid for the whole solution domain and outlines the effects of most important operating, geometrical and material parameters on electronic potential. (C) 2013 Elsevier Ltd. All rights reserved.