A detachable DC power source includes: a reference surface extending in front-rear and left-right directions; support walls protruding upward from opposite ends of the reference surface and extending in the front-rear direction; battery-side rails protruding outward in the left-right direction from the upper ends of the pair of support walls and extending in the front-rear direction; and a first battery-side distinguishing region disposed between the support walls in the left-right direction and at a connection location between the reference surface and one of the support walls. A first battery-side distinguishing member is provided in the first battery-side distinguishing region and is directly connected to the one the support walls and to the reference surface. The detachable DC power source may be used to power an electrical device having a first device distinguishing part capable of receiving the first battery distinguishing member.