To provide double protection during charging in a battery pack used as a power supply of an electric apparatus.

The battery pack 100 includes a module group wherein a plurality of battery modules 112 are connected in series and a main controller 134 that is connected to the module group and controls charging thereof. Each of the battery modules includes a cell group wherein a plurality of battery cells are connected and a module controller that is connected to the cell group and controls charging thereof. The battery pack also includes an energy storage unit that is connected to the module group and thereby can be charged therefrom. The main controller determines whether at least one of the plurality of module controllers corresponding to the plurality of modules stops charging, and when it determines that at least one of the module controllers stops charging, it instructs the other module controllers that does not stop charging to stop charging and enables operation using the energy storage unit.