In this paper, a polymer electrolyte fuel cell system is modeled in order to investigate the following operational modes: transient and nominal operations and rejuvenation process. As a preliminary investigation, the Ballard NEXA™ power module performances are experimentally characterized. The power consumptions of ancillaries, such as the air fan, are then evaluated to investigate the system. To achieve an overall system model, components, such as the compressor, the pipes, the valves, the expander, and the humidifier, are then simulated. This simulation is based on the same assumption: Fluidic circuits are described by an electrical analogy. The anodic gas management is finally described according to the delivered output current.