A battery system comprises a plurality of battery modules, each of the battery modules includes an assembled battery configured to include a plurality of battery cells connected in series, a monitoring unit configured to monitor the assembled battery, and an external member configured to be electrically connected to the monitoring unit, and the monitoring unit of each of the battery modules has a generation unit configured to generate, based on an electric signal input from the external member, an identification information item on the corresponding one of the battery modules, the identification information items of the respective battery modules being different from one another.