In a battery system including an assembled battery having a plurality of battery cells connected in series, each of a plurality of monitoring units includes a voltage classification unit configured to classify a terminal voltage between each pair of input terminals in the monitoring unit as a cell voltage or as a zero voltage that is a terminal voltage of substantially zero. The input terminals in each of all or all but one of the monitoring units include at least one specific terminal pair for acquiring the zero voltage at a different position and/or include a different number of specific terminal pairs for acquiring the zero voltage. Each of the plurality of monitoring units further includes an identifier generation unit configured to generate an identifier based on at least one of the position of the at least one specific terminal pair and the number of specific terminal pairs.