A battery device includes a battery pack, a circuit substrate which acquires battery information on the battery pack or controls charge and discharge of the battery pack, a switch including a first power element or a second power element, and a heat radiator. The switch is a device controlling input and output of electric power to and from the battery pack, and an exterior part of the switch is arranged away from the circuit substrate. The heat radiator is a member made of a material having thermal conductivity, and is in direct contact with or indirect contact via a heat conductor with the exterior part of the switch so that heat of the switch can be transferred.