Hybrid hydrogen-electric UAV propulsion system combining PEM fuel cell and battery pack for extended flight endurance and reduced emissions. The H2 tank feeds a PEM fuel cell whose output passes through a DC-DC converter to a shared DC bus, while a battery pack with its own DC-DC converter provides peak power and stabilization. An EMS controller manages power distribution between fuel cell and battery, receiving sensor feedback from both sources to optimize thrust delivery to the electric motor and propeller. This architecture demonstrates fuel cell-battery hybridization for aerospace applications, balancing energy density with power response. Fork this diagram on Diagrams.so to customize converter specifications, add thermal management loops, or integrate battery management system details.