TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Device: The cell voltage monitor further comprises a reference thermistor in series with the sensing thermistor and thermally isolated from the heating resistor. The reference thermistor and the sensing thermistor have the same resistance as a function of temperature characteristics. A diode is electrically connected at one end between the series-connected sensing and reference thermistors.The resistance of the sensing thermistor changes with an increase in temperature above ambient. The sensing thermistor is a resettable thermal switch or a polymeric positive temperature coefficient fuse. The heating resistor is a positive temperature coefficient thermistor. The voltage monitor comprises several voltage monitors. The series-connected heating resistors and rectifiers in each of the voltage monitors are connected in series.The series-connected reference thermistors and sensing thermistors in each voltage monitor are connected in parallel across a reference voltage supply, and the other ends of the diodes in each voltage monitor are connected to a common signal line. The polarity of the diodes is such that current is prevented from flowing from an unheated one of the sensing thermistors to a heated one via the common signal line.The resettable thermal switches in each voltage monitor are connected in parallel. The voltage monitors are mounted on a flexible printed circuit board. The polarity of the rectifier is such that current is prevented from flowing through the series-connected resistor and rectifier when the fuel cell is in voltage reversal.Preferred Method: The signal is obtained by connecting a reference thermistor in series with and thermally isolated from the sensing thermistor, applying a reference voltage across the series-connected sensing and reference thermistors, and measuring the voltage across the sensing thermistor.The method further comprises thermally isolating the sensing thermistor from the fuel cell stack.    TECHNOLOGY FOCUS - POLYMERS - Preferred Materials: The heating resistor, rectifier, and sensing thermistor are each coated with a thermosetting polymer. The fuel cells in the stack are solid polymer electrolyte fuel cells.