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The growing popularity and success of fuel cells (FCs) in aerospace, stationary power, and transportation applications is driving and challenging researchers to complement and in some cases altogether replace the batteries of portable systems in the hopes of increasing functional density, extending runtime, and decreasing size. Direct-methanol fuel cell (DMFC) batteries have now been built and conformed to low-cost technologies and chip-scale dimensions. Conventional FC models, however, fail to accurately capture the electrical nuances and runtime expectancies of these microscale devices, yet predicting that these electrical characteristics are even more critical when designing portable low-power electronics. A Cadence-compatible model of a DMFC battery is therefore developed to capture all pertinent dynamic and steady-state electrical performance parameters, including capacity and its dependence to current and temperature, open-circuit voltage, methanol-crossover current, polarization curve and its dependence to concentration, internal resistance, and time-dependent response under various loading conditions-the model can also be extended to other micro- and macroscale FC technologies. The simulation results of the proposed electrical model are validated and compared against the experimental performance of several DMFC prototypes, resulting in a runtime error of less than 10.8% and a voltage error under various current loads of less than 80 mV for up to 95% of its operational life. The root cause of the remaining errors and relevant temperature effects in the proposed model are also discussed.