A rechargeable battery pack includes a rechargeable battery, a mount frame wrapping at least part of the rechargeable battery, an outer case wrapped around the mount frame, the outer case including a first case including a first protrusion portion protruding therefrom, and a second case having a second protrusion portion protruding therefrom, the first protrusion portion being fixed to the second protrusion portion, and a protective circuit module electrically connected to the rechargeable battery.