A vehicle battery device includes a plurality of battery cell groups in which battery cells are connected in series, connection switches which can switch an electrical connection between the pluralityof battery cell groups to a series connection or a parallel connection, and current sensors which detect electric currents flowing in the respective battery cell groups in both of the series connection and the parallel connection, and the current sensor is provided in the vicinity of a positive electrode terminal or a negative electrode terminal of each of the battery cell groups.