Battery-powered automobiles are emerging as a promising alternative to internal combustion engine vehicles in response to the internationally strengthening regulation on carbon dioxide emissions. Due to the heavy weight of the electric drive unit, the weight savings of the electric vehicles are often attempted on body structures by using lightweight materials such as fiber-reinforced composites with traditional metal alloys. In the present study, a new multi-material design of a battery pack structure is proposed and its performance is evaluated through random vibration fatigue tests. The fatigue tests are virtually performed on a full-scale finite element model of the battery pack. The virtual tests embody boundary and loading conditions required by a real industry specification. The vibration loading is specified in the form of a power spectral density and the fatigue analysis is conducted accordingly in frequency domain. The cumulative fatigue damage and lives of each component composing the batter pack structure are predicted. The present modeling approach could benefit the preliminary design of an automotive body structure because the performance evaluation on various prototypes can be efficiently conducted without a physical model.