Patent ID: 7962300

Claim:
A battery state judging method of a lead-acid battery loaded on a vehicle, comprising the steps of: obtaining, in advance, a DC internal resistance r 0 of a lead-acid battery in a substantially non-deteriorated and fully-charged state; calculating, in advance, a load R imposed at an engine starting time, using a following Equation (1), from an open-circuit voltage OCV 0 and a lowest voltage Vst 0 at the engine starting time, both measured when the lead-acid battery is in a substantially non-deteriorated and fully-charged state, and the DC internal resistance r 0 ; calculating a DC internal resistance r of the lead-acid battery, using a following Equation (2), from an open-circuit voltage OCV and a lowest voltage Vst at an engine starting time, both measured when the lead-acid battery is in a deteriorated or insufficiently-charged state, and the calculated load R imposed at the engine starting time; and judging a state of the lead-acid battery by comparing the DC internal resistance r with the DC internal resistance r 0 ; R=r 0 ×Vst 0 /( OCV 0 −Vst 0 ) (1) r=R ×( OCV−Vst )/ Vst (2).