Patent ID: 8288996

Claim:
An apparatus for estimating a state of charge of a rechargeable battery charged by a vehicle-mounted power generation apparatus capable of generating a variable output voltage, comprising a configuration to perform: a detecting function of detecting a charging/discharging current of said rechargeable battery; and an estimating function of making an estimation of said state of charge on the basis of relationship data defining relationship among said output voltage, said state of charge, a convergence value to which said charging/discharging current converges through transient behavior thereof depending on a polarization state of said rechargeable battery in a state where variation of said output voltage is below a predetermined value after said output voltage is changed, and a plurality of values of said charging/discharging current during said transient behavior detected by said detecting function using a characteristic of the rechargeable battery that the charging/discharging current transiently converges to the convergence value with dissolution of the polarization state due to change of the output voltage.