Patent ID: 7471090

Claim:
A method of determining a capacity of a lead-acid battery comprising: providing a lead-acid battery having at least one cell; fully charging the lead-acid battery; applying a predetermined current ramp to the fully charged lead-acid battery while measuring a battery terminal voltage comprising applying a linearly increasing current ramp to the lead-acid battery while measuring a battery terminal voltage, wherein the increasing current ramp has a slope and applying a decreasing current ramp to the lead-acid battery while measuring a battery terminal voltage after the battery terminal voltage reaches a safe limit, wherein the decreasing current ramp has a same slope as an absolute value of the increasing current ramp, wherein the slope of the linearly increasing current ramp is about 0.33 A/sec; calculating an I up , wherein the I up is a transition current from charging to overcharging; determining a battery specific gravity of the lead-acid battery; and calculating the capacity of the lead-acid battery dependent upon the determined battery specific gravity using a correlation function, wherein the correlation function is Capacity=(I up ×27.58)−45.35 when the full charge specific gravity is about 1.30 or Capacity=(I up ×28.95)−36.97 when the battery specific gravity is about 1.28.