Abstract: A sub battery for easily charging includes: a battery body including a first surface facing toward a first direction and a second surface facing toward a second direction opposite the first direction, and an opening formed on at least a portion between the first and second surfaces; a holder having a charging connector cable attachably and detachably fixed thereto, and movably disposed in the opening; and a locking device mounted between the holder and the battery body to fix the holder to the battery body in a closed state, and to unlock the holder according to a movement of the holder by a first distance.