Fuel cell systems, e.g. systems including proton exchange membrane (PEM) fuel cells, are engineered to have more than one internal electrical resistance that can change according to temperature. Such changes in internal electrical resistance levels allow rapid heat-up of the fuel cells from low temperatures to an elevated temperature that is optimal for water management and fuel cell operation. The fuel cell systems can include at least one fuel cell and at least one resistor-switch unit electrically connected to the at least one fuel cell. The at least one resistor-switch unit includes a resistor and a switch in which the switch is electrically connected in parallel with the resistor.