Battery pack

A battery pack includes a housing, a plurality of assembled batteries disposed in the housing, obtaining units arranged one for each of the assembled batteries in the housing, and the monitoring device equipped with a master antenna. The obtaining units obtain battery information about the assembled batteries and transmit it to the master antenna of the monitoring device through wireless communication using slave antennas. The master antenna and/or the slave antennas are each implemented by a directional antenna which emits a radio wave to be higher in power in a given directional direction than in a given undirectional direction. This minimizes a risk of a communication failure arising from radio wave interference.