Based on increasing component efficiencies and the ongoing drivetrain electrification the influence of the auxiliary load raises. Up to now, the effect of the additional energy consumption of auxiliary loads, such as the HVAC system, is often not investigated in detail. To close this gap for various fuel cell based drivetrains this paper applies a novel approach of Hollweck [1] and analyzes the holistic energy demand under realistic boundary conditions with a validated total vehicle simulation model. Thereby the drivetrains of a midsized fuel cell electric vehicle (FCEV), fuel cell plug-in electric vehicle (FC-PHEV) as well as the fuel cell range-extended electric vehicle (FC-REEV) are considered. In a first step, the novel approach, which regards the influence of the user behavior, the vehicle properties, the climate boundaries and the starting conditions is introduced. In a second step, the total vehicle simulation model consisting of the vehicle architecture, the drivetrain topology with its electrical and mechanical components, the thermal management of the drivetrain and the thermal management of the vehicle cabin is explained, verified and parameterized. In a final step, the seasonal and yearly energy demand for different driving profiles (urban, rural and motorway) and German weather conditions as well as the influence of colder winter conditions is analyzed. The detected varying auxiliary loads' influence on the different fuel cell based drivetrains is shown and discussed. Thereby, one of the results is that the auxiliary loads' impact on FCEVs is moderate, while the impact on FC-PHEVs and FC-REEVs - driven in battery- mode is significant. Especially in cold winter conditions this effect is substantial. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.