Battery capacity calculation method

A method for determining battery capacity comprising the steps of:

• a) measuring an initial value V.sub.0 of a terminal voltage of a battery to obtain an initial state of charge condition value S.sub.0 of an indication value S indicative of a state of charge condition of the battery, in which S is defined to be equal to 0 when the battery is fully charged and is defined to be equal to 1 when the battery is effectively discharged;
• b) determining a subsequent value V.sub.i of a terminal voltage after a time interval .DELTA.t and estimating a discharge current value I based on the determined subsequent value V.sub.i ;
• c) calculating a change .DELTA.S.sub.0 in the initial value state of charge condition S.sub.0 of the battery over the time interval .DELTA.t as a function of the discharge current value I and the initial state of charge condition indication value S.sub.0 using the following equation:
• .DELTA.S.sub.0 =I.sub.i .times..DELTA.t.times.f(I.sub.i, S.sub.0).div.M
• wherein an average battery discharge current corresponding to said discharge current value I is I.sub.i, where f(I.sub.i,S.sub.0) is a function such that when S.sub.0 =0 f(I.sub.i,S.sub.0)=.times.1;
• when S.sub.0 =1, f(I.sub.i,S.sub.0)=1 if I.sub.i is low, f(I.sub.i S.sub.0)=(I.sub.i .div.I.sub.0).sup.Y if I.sub.i is high, and f(I.sub.i,S.sub.0) increases monotonically when S.sub.0 is increased from 0 to 1;
• and M, I.sub.0, and Y are constants depending on the battery;
• d) updating the state of charge condition by calculating a current state of charge condition value S.sub.i of the indication value S, wherein S.sub.i =S.sub.0 +.DELTA.S.sub.0 ;
• e) repeating step b;
• f) calculating a change .DELTA.S.sub.i in the current state of charge condition value S.sub.i of the battery over the time interval .DELTA.t as a function of the discharge current value I.sub.i and the state of charge condition indication value S.sub.i using the following equation;
• .DELTA.S.sub.i =I.sub.i .times..DELTA.t.times.f(I.sub.i, S.sub.i).div.M
• wherein f(I.sub.i,S.sub.i) is a function such that when S.sub.i =0, f(I.sub.i,S.sub.i)=1;
• when S.sub.i =1, f(I.sub.i S.sub.i)=1 if I.sub.i is low, f(I.sub.i S.sub.i)=(I.sub.i .div.I.sub.0).sup.Y if I.sub.i is high, and f(I.sub.i,S.sub.i) increases monotonically when S.sub.i is increased from 0 to 1;
• and M, I.sub.0, and Y are constants depending on the battery;
• and
• g) updating the state of charge condition by calculating a new value S.sub.i+1 of the indication value S indicative of a new state of charge condition of the battery from the equation:
• S.sub.i+1 =S.sub.i +.DELTA.S.sub.i.