A method for operating a direct methanol fuel cell (DMFC) at variable power levels and protecting the DMFC from transient variations in ambient temperature, said method comprising: (a) arranging a DMFC stack so that denuded air exiting the stack drains downward and all fuel exiting the stack flows upward; (b) continuously monitoring voltage of a stack, section and/or single cell of the DMFC; (c) interrupting continuous operation of the DMFC suddenly and observing voltage decay; (d) assessing cell and stack conditions and/or methanol demand based upon the measured voltages via the algorithm F MeOH _ Dose = F stoich + F cross + F Temp + F du / dt, wherein F MeOH_Dose is the amount of pure methanol supplied to the anode mixing chamber of the DMFC fuel cell, F stoich is the amount of methanol reactant to be supplied to the anode mixing chamber of the DMFC fuel cell due to consumption by current supply and evaporation losses, F cross is the amount of methanol supplied to the anode mixing chamber of the DMFC fuel cell in order to compensate for methanol diffusion from anode to cathode, F Temp is the amount of methanol required to maintain a stack configuration at a selected operating temperature, and F du / dt is the amount of reactant methanol available at the anode as determined by the cell potential during a diagnostic current step or alternatively by a perturbation of fuel and oxidant flow; and (e) correctively adjusting methanol concentration of the DMFC. (a) arranging a DMFC stack so that denuded air exiting the stack drains downward and all fuel exiting the stack flows upward; (b) continuously monitoring voltage of a stack, section and/or single cell of the DMFC; (c) interrupting continuous operation of the DMFC suddenly and observing voltage decay; (d) assessing cell and stack conditions and/or methanol demand based upon the measured voltages via the algorithm F MeOH _ Dose = F stoich + F cross + F Temp + F du / dt, wherein F MeOH_Dose is the amount of pure methanol supplied to the anode mixing chamber of the DMFC fuel cell, F stoich is the amount of methanol reactant to be supplied to the anode mixing chamber of the DMFC fuel cell due to consumption by current supply and evaporation losses, F cross is the amount of methanol supplied to the anode mixing chamber of the DMFC fuel cell in order to compensate for methanol diffusion from anode to cathode, F Temp is the amount of methanol required to maintain a stack configuration at a selected operating temperature, and F du / dt is the amount of reactant methanol available at the anode as determined by the cell potential during a diagnostic current step or alternatively by a perturbation of fuel and oxidant flow; and F MeOH_Dose is the amount of pure methanol supplied to the anode mixing chamber of the DMFC fuel cell, F stoich is the amount of methanol reactant to be supplied to the anode mixing chamber of the DMFC fuel cell due to consumption by current supply and evaporation losses, F cross is the amount of methanol supplied to the anode mixing chamber of the DMFC fuel cell in order to compensate for methanol diffusion from anode to cathode, F Temp is the amount of methanol required to maintain a stack configuration at a selected operating temperature, and F du / dt is the amount of reactant methanol available at the anode as determined by the cell potential during a diagnostic current step or alternatively by a perturbation of fuel and oxidant flow; and (e) correctively adjusting methanol concentration of the DMFC.