HELION develops high efficiency, autonomous, onboard fuel cell systems matched to the required power via 2 different technologies, H2/O2 technology intended for extreme milieu and H2/air technology for transportation (captive fleets). Onboard electrical generators are confronted by operating and environmental conditions that are particularly difficult: Large movement constraints Vibration linked to movement over surfaces, for example Operating conditions implying extremes of heat or cold Onboard electrical generators based on fuel cells are competitive with other generator solutions, notably due to their carefully controlled integration by HELION. Technologies employing several stacks in parallel and/or hybridisation technologies with batteries and super capacitors allow several power ranges for varied applications. Lastly, the yields offered by PEM fuel cells exceed those of heat engines and these systems can offer a propulsion autonomy that is more than double that of traditional batteries.