In this paper, the convergence properties of the finite element approximation of the thermistor problem are investigated, both from theoretical and numerical point of view. From one hand, based on a duality argument, a theoretical convergence result is proved under low regularity assumption. From other hand, numerical experiments are performed based on a decoupled algorithm. Moreover, on a non convex domain, the convergence properties versus the mesh size are shown to be improved by using suitable mesh adaptation strategy and error estimator.