To solve problems in a lead-acid battery for an automobile that the discharging frequency of the lead-acid battery is high caused by high idling stop frequency, and in a using condition with decreased charging chance, life is shortened and charging becomes insufficient.

This lead-acid battery uses a positive plate having a positive active material density of 3.5 to 4.5 g/cc, dilute sulfuric acid having a specific gravity of 1.24 to 1.25 (20°C) in a full charge state as an electrolyte, and carbon which is an additive of a negative plate of 0.5 to 2.0% per the amount of a negative active material.