A battery including an output terminal, an electric storage device, a monitoring apparatus including a detector and a controller, the detector being configured to detect a variation value corresponding to an amount of charge of the electric storage device, a relay connected to the output terminal and the electric storage device, and a communication unit connected to the controller. The controller is configured to execute an opening process to switch a state of the relay from a closed state to an open state and to cause the communication unit to receive an input signal from outside.