A secondary battery is implemented as an assembly of a plurality of battery modules. An ECU calculates a deterioration indicator quantitatively indicating a degree of deterioration of a battery module for each of the plurality of battery modules, and detects as a module to be replaced, a battery module of which deterioration indicator has reached a prescribed replacement level. The ECU further extracts a module to additionally be replaced, which should be replaced simultaneously with the module to be replaced above, from battery modules of which deterioration indicator has not reached the replacement level, among the plurality of battery modules.