Abstract: A battery measurement system includes: a battery including terminals and a housing case, and a battery measurement device. The battery measurement device includes: a signal control unit provided on a first electrical path connecting positive and negative electrode external terminals and configured to receive or apply an AC signal, a response signal input unit provided on a second electrical path connecting positive and negative electrodes of an electrode body and configured to receive a response signal to the AC signal, and a calculation unit configured to calculate complex impedance information based on the response signal. The second electrical path is wired from the response signal input unit toward the inside of the housing case so that a magnetic flux passage area surrounded by the electrode body and the second electrical path is smaller in magnitude than an area surrounded by the electrode body, the terminals and the housing case.

Abstract: A fuel cell has multiple cells, the multiple cells including a first cell having a first fuel gas flow path, and a second cell having a second fuel gas flow path and a sensor that measures a specific parameter value relating to a decrease in concentration of fuel gas in the second fuel gas flow path.

Abstract: A fuel cell stack includes: a first cell having a first fuel gas flow path; and a second cell having a second fuel gas flow path constructed to have a specific flow path structure having a higher potential for a decrease in concentration of a fuel gas than that of the first fuel gas flow path during power generation. A sensor is located on the second cell to detect a decrease in concentration of the fuel gas during power generation. In one exemplified structure, a groove formed on an anode separator of the second cell as the second fuel gas flow path has a restriction element to narrow the sectional area of flow passage. A hydrogen concentration sensor is located in a non-narrowed area in the downstream of the restriction element having a lower pressure level. Impurity gas discharge control discharges an anode off gas out of the fuel cell stack, in response to detection of a decrease in hydrogen concentration to or below a preset reference level by the hydrogen concentration sensor.