A battery is provided. The battery includes a positive electrode including a positive electrode active material layer provided on a positive electrode current collector; a negative electrode; and a separator at least including a porous film, wherein the porous film has a porosity ε [%] and an air permeability t [sec/100 cc] which satisfy formulae of: t=a×Ln(ε)−4.02a+100 and −1.87×1010×S−4.96≦a≦−40 wherein S is the area density of the positive electrode active material layer [mg/cm2] and Ln is natural logarithm.