A battery assembly includes: a receptacle connector including a receptacle contact with a bolt hole for bolting formed therein, a receptacle housing attached to the receptacle contact; a battery having an upper surface on which the receptacle contact of the receptacle connector is attached by the bolting, and a right side surface roughly perpendicular to the upper surface. The receptacle housing of the receptacle connector is formed so as to extend in an elongated shape along the tangent direction of an imaginary circle C centered on the central axis of the bolt hole of the receptacle contact of the receptacle connector as viewed in the central axis direction of the bolt hole, and is capable of coming into contact with the right side surface of the battery at the time of the bolting.