Patent ID: 8040108

Claim:
A state-of-charge estimation apparatus for estimating a charged state of a rechargeable battery chargeable by a vehicle-mounted power generation apparatus whose output voltage is variable, comprising: a history quantification means to quantify a history of charging and discharging of said rechargeable battery; and an estimation means to estimate the charged state based on a parameter representing a charging/discharging current of said rechargeable battery when variation of said output voltage of said vehicle-mounted power generation apparatus is below a predetermined value, and said history of charging and discharging history inputted thereto; wherein the estimation means includes a means to calculate a necessary time necessary for said charging/discharging current to converge to a convergence value depending on said output voltage based on said history of charging and discharging history and a means to estimate the charged state of said rechargeable battery based on a value of said parameter after a lapse of said necessary time.