A battery device includes a battery cell, a case housing the battery cell, an antenna, a battery-side communication unit performing wireless communication with an electronic-apparatus side communication unit provided at an electronic apparatus on which the battery device is removably mounted through the antenna, a memory unit storing battery data which is data concerning the battery device and a control unit performing control of the battery-side communication unit, both reading/writing of the battery data with respect to the memory unit or only reading thereof.