A battery pack includes a battery side terminal electrically connectible with a device side terminal of a device body that may be a tool body of an electric tool or a charger body of a charger. The battery side terminal includes a first contact portion and a second contact portion. The first contact portion configured to form an electric contact through contact with a first side surface of the device side terminal. The second contact portion configured to form an electric contact through contact with a second side surface opposite to the first side surface of the device side terminal. The first contact portion configured to contact the first side surface in a first contact range having a first length. The second contact portion configured to contact the second side surface in a second contact range having a second length that may be different from the first length.