A battery unit includes: a main accommodation casing that includes a power output terminal; at least one sub-module that is accommodated in the main accommodation casing; and a control unit that is accommodated in the main accommodation casing and controls at least one of charging and discharging of a unit battery, wherein in the sub-module, two or more battery blocks are accommodated inside a sub-accommodation casing so that the terminals of the battery blocks each including a plurality of unit batteries are not exposed and the battery blocks are connected to each other through an electric connection member.