An auxiliary battery storage device for storing an auxiliary battery that is used for performing cell balancing to a main battery adopted in an electric vehicle or supplying power to the main battery having low state of charge, SOC, the auxiliary battery storage device comprising: a case body formed in a box shape with an open top portion to have an inner space in which the auxiliary battery is stored; a case body cover coupled to the case body to open or close the open top portion of the case body; characterized in that said auxiliary battery storage device further comprises: a terminal connection member fixed to an inner surface of the case body cover to contact a power terminal of the auxiliary battery when the top portion of the case body is closed by the case body cover; and a power cable configured to extend from the terminal connection member to the main battery, the case body has hooking grooves formed in side plates (11, 12) thereof facing each other, and the case body cover has hooking protrusions engaged with the hooking grooves so that the case body and the case body cover are coupled to each other, the hooking protrusions are respectively moved by an electromagnetic force to be engaged with or disengaged from the hooking grooves, and the case body cover includes: an electromagnet disposed at a position spaced apart from the hooking protrusion by a predetermined distance to pull the hooking protrusion by an electromagnetic force to be disengaged from the hooking groove; and a spring configured to elastically bias the hooking protrusion toward the hooking groove so that the hooking protrusion is engaged with the hooking groove. a case body formed in a box shape with an open top portion to have an inner space in which the auxiliary battery is stored; a case body cover coupled to the case body to open or close the open top portion of the case body; characterized in that said auxiliary battery storage device further comprises: a terminal connection member fixed to an inner surface of the case body cover to contact a power terminal of the auxiliary battery when the top portion of the case body is closed by the case body cover; and a power cable configured to extend from the terminal connection member to the main battery, a terminal connection member fixed to an inner surface of the case body cover to contact a power terminal of the auxiliary battery when the top portion of the case body is closed by the case body cover; and a power cable configured to extend from the terminal connection member to the main battery, the case body has hooking grooves formed in side plates (11, 12) thereof facing each other, and the case body cover has hooking protrusions engaged with the hooking grooves so that the case body and the case body cover are coupled to each other, the hooking protrusions are respectively moved by an electromagnetic force to be engaged with or disengaged from the hooking grooves, and the case body cover includes: an electromagnet disposed at a position spaced apart from the hooking protrusion by a predetermined distance to pull the hooking protrusion by an electromagnetic force to be disengaged from the hooking groove; and a spring configured to elastically bias the hooking protrusion toward the hooking groove so that the hooking protrusion is engaged with the hooking groove. an electromagnet disposed at a position spaced apart from the hooking protrusion by a predetermined distance to pull the hooking protrusion by an electromagnetic force to be disengaged from the hooking groove; and a spring configured to elastically bias the hooking protrusion toward the hooking groove so that the hooking protrusion is engaged with the hooking groove.