Abstract: A cell voltage monitoring device is powered internally by the stack being measured and uses no external power sources whatsoever. The cell voltage monitoring device comprises a plurality of differential amplifiers each corresponding to a cell within the stack. The differential amplifiers are divided into groups of a suitable number, each group corresponding to a set of series-connected cells being collectively measured by the differential amplifiers in that group. Within each group of differential amplifiers, the positive supply terminal of each differential amplifier is connected to the most positive output terminal of the corresponding set of series-connected cells, and the negative supply terminal of each differential amplifier is connected to the most negative output terminal of the corresponding set of series-connected cells. By doing so, each group of differential amplifiers is powered by the set of series-connected cells being measured by that group.