A battery pack, a vehicle, and an energy storage device. The battery pack includes a housing with a first direction and a second direction perpendicular to the first direction. The battery pack housing includes at least one rectangular cell accommodating unit is formed therein. The battery pack also includes a plurality of rectangular cells, and has a dimension greater than or equal to 600 mm along the first direction. The plurality of rectangular cells are arranged in the rectangular cell accommodating unit along the second direction. The rectangular cell has a thickness of D, length of L, and height of H. A length direction of at least one rectangular cell extends from one side of the rectangular cell accommodating unit to its other side along the first direction, and meets: L>H, L>D, 600 mm≤L≤2500 mm, 23≤L/D≤208.