Hydrogen-powered low-temperature fuel cells (PEFCs) are the energy conversion units in vehicles with methanol as the energy carrier and a power train consisting of the following main units: methanol reformer (H-2 production) including catalytic converter, gas treatment, PEFC with peripheral units, electric motor with electric controllers and gearbox. The process engineering analysis is based on a simulation model and describes the energy and water management as a function of different assumptions as well as operating and ambient conditions for net electricity generation in a PEFC-powered power train. In particular, it presents an approach for balancing both water recovery (PEFC) and the use of water for the methanol reforming process as well as for the humidification of the PEFC. The overall balances present an optimised energy management including peripheral air compression for the PEFC.