Disclosed is a lead-acid battery including: a battery container; an electrolyte and an electrode plate group in the battery container; and a battery container cover that hermetically seals an opening of the battery container, wherein the electrode plate group includes a positive electrode plate including a positive electrode active material, a negative electrode plate including a negative electrode active material, and a separator interposed between the positive electrode plate and the negative electrode plate, the battery container cover is provided with a liquid port, a liquid port plug that closes the liquid port, and a sleeve that hangs down from the liquid port to a prescribed liquid surface height of the electrolyte, a sodium ion concentration contained in the electrolyte is 1 mmol/L to 90 mmol/L, and a specific surface area of the positive electrode active material is 5 m2/g to 9 m2/g.