Problem detection apparatus

An assembled battery system comprising:

• an assembled battery that is comprised of battery blocks connected in series;
• a relay that is provided between the assembled battery and an external circuit, both of which are in a high voltage system, the relay configured to switch an electrical connection state of the assembled battery to the external circuit between a closed state and an open state;
• a measurement circuit that measures a voltage of a circuit in the high voltage system, the measurement circuit being in the high voltage system and being connected between the relay and the external circuit;
• and
• a controller that detects, based on the voltage measured by the measurement circuit, whether or not the relay has a short circuit, in a case where a command to switch the relay to the open state has been output, the controller being in a low voltage system having a lower voltage than a voltage of the high voltage system.