A battery pack including a battery cell, a circuit board electrically connected to the battery cell, a first cover, and a second cover. The battery cell includes a battery element, a rectangular first packaging component, a recess, and a rectangular second packaging component. The battery element is housed in the recess, the first packaging component and the second packaging component are stacked so that the second packaging component covers the opening of the recess, the periphery of the opening is sealed, both ends of the second packaging component are abutted at the outer bottom surface of the recess of the first packaging component, and the first outer resin layer and the second inner resin layer are bonded by heat seal adhesive layer.