In this paper, both a theoretical and an experimental study of the dynamic performance of a commercial fuel cell are described. The analysis has been focused in the start up and shutdown processes because they allow analysing the influence of different parameters. In this sense, the evolution of the stack and the environment temperatures can be observed, which allows measuring the heat released by the fuel cell. Moreover, the analysis of the flow of hydrogen and air allow obtaining various models for simulating the fuel cell system. Finally, the graphics associated with the variation of the stack voltage and current make possible to obtain the characteristic equations of these fuel cell systems, in order to provide power for auxiliary devices when the battery is not operating.