Patent ID: 7078907

Claim:
A battery capacity calculating method for calculating a residual capacity and/or residual power of a secondary battery, comprising: calculating an equilibrium voltage curve C equ showing a relation between a discharged capacity and an equilibrium voltage in said secondary battery; measuring a terminal voltage V mea and a current value I of said secondary battery at a time of discharging; calculating a discharged capacity Q mea of said secondary battery based on the terminal voltage V mea and the current value I; calculating an apparent equilibrium voltage V ocv by adding a voltage drop ΔV dc by a direct current resistance R dc to the terminal voltage V mea ; calculating an apparent discharged capacity Q ocv corresponding to the apparent equilibrium voltage V ocv calculated based on the equilibrium voltage curve C equ ; calculating a capacity shift ΔQ being a difference between the discharged capacity Q mea and the apparent discharged capacity Q ocv ; and estimating a discharge curve C pre in a future based on the capacity shift ΔQ calculated at said capacity shift calculating step.