In a battery system, a battery module includes a plurality of cells. A management unit manages charging-discharging of the battery module and a temperature inside the battery module. The management unit estimates a maximum temperature of an inside of a cell in the battery module based on a measured temperature in the battery module, and controls, during charging-discharging of the battery module, a charging-discharging current of the battery module and/or cooling of the battery module in such a way that the estimated maximum temperature does not exceed an upper limit temperature.