In accordance with various embodiments, there is a method for determining the capacity of a battery. Various embodiments include applying a predetermined current ramp to a fully charged lead-acid battery while measuring a battery terminal voltage. An I.sub.up can be determined, where the I.sub.up is a transition from charging to overcharging. A specific gravity of the lead-acid battery can also be determined. The capacity of the lead-acid battery can then be determined from the I.sub.up using a correlation function that describes the relationship of the I.sub.up to the capacity, where the correlation function depends on the specific gravity of the lead-acid battery.