This paper presents a gray-box equivalent circuit model (ECM) in order to predict the performance of direct methanol fuel cell (DMFC) unit. The ECM is composed of electronic components ranging from operational amplifier resistors to diodes. The current-voltage profiles and current-power profiles of this ECM are validated by the simulation results of the COMSOL model. Afterward, the influences of methanol concentration, operating temperature, and oxygen concentration on the performance of the single passive DMFC are all validated experimentally. All validations show that the ECM provides a good approximation of the behavior of the DMFC. In addition, a simulated application of a circuit system employing the ECM is explained. The simulated result is validated experimentally. This research makes it possible to analyze the behavior of a DMFC in real applications.