LEAD-ACID BATTERY

A lead-acid battery (1) includes an electrode group (11) in which a plurality of positive electrode plates (3) and a plurality of negative electrode plates (2) are stacked via a separator (4), a cell chamber (14) storing the electrode group (11), and an electrolyte solution. The electrolyte solution contains 0.03 to 0.3 mol/L of Na. When two electrode plates, the positive electrode plate or the negative electrode plate (end plate), located at both ends of the electrode group (11) are disposed close to inner walls of a cell chamber (14), an inter-electrode gap W obtained by W = (L - d1)/N - d2 is -0.1 to + 0.15 mm, where a maximum separation distance between the surfaces of both end plates facing the inner walls of the cells is L, a total of thicknesses of the positive electrode plates (3) and the negative electrode plates (2) in the electrode group (11) is d1, the number of inter-electrode gaps in the cell chamber (14) is N, and a total thickness of the separator interposed between the positive electrode plate and the negative electrode plate is d2. The separator (4) has a first rib on the negative electrode plate side.