Electric and hybrid electric vehicles use valve-regulated lead acid (VRLA) cells that are subjected to dynamic operation with charge, rest, and discharge periods in the order of seconds. Such operation requires more sophisticated models that incorporate the electrochemical double layer. While this effect has been incorporated in a handful of electrochemical systems, the lead-acid cell, with its sluggish reaction kinetics, is one of the few where it is significant. This significance is demonstrated with use of the current-interrupt technique, where the model is used to provide guidelines for the estimation of various resistances. The usefulness of the modeling approach is exemplified by its ability to explore the effect of changing electrochemical area and concentration with state of charge, and the role of parasitic side reactions in the voltage response of the cell. Simulations of pulse charging and dynamic stress test of VRLA cells, where considerable differences are shown when including the double layer, illustrate the need for modifying the presently used modeling approach. In addition, simulations are compared to current-interrupt experiments on commercial cells in order to evaluate the applicability of the model and to identify the differences. (C) 2003 The Electrochemical Society.