A battery pack including a plurality of battery modules; a tray including an interior space where the plurality of battery modules are positioned; a plurality of beam frames traversing an upper surface of the tray to partition spaces where the plurality of battery modules are positioned; and a plurality of heatsinks having a hollow structure through which a coolant flows, wherein each heatsink is coupled to a part of a respective one of the plurality of beam frames and faces a side surface of a respective one of the plurality of battery modules, at least one drainage hole is provided at the tray and at least one drainage hole is provided at the beam frame, and the at least one drainage hole of the tray and the at least one drainage hole of the beam frame are provided below the heatsink.