Patent ID: 8244449

Claim:
An apparatus for detecting a state of a battery serving as a power source for cranking an internal combustion engine, the apparatus comprising: a detecting unit configured to detect a current and a voltage of the battery during a cranking period of the internal combustion engine, and output a parameter associated with at least one of the detected current and voltage of the battery; and an internal resistance calculating unit configured to, when a degree of change in the parameter within each of a plurality of specified periods included in the cranking period is equal to or greater than a predetermined threshold: (i) calculate a local internal resistance of the battery based on first values of the current and voltage for a corresponding one of the plurality of specified periods, the first values of the current and the voltage being detected within each of the plurality of specified periods, the local internal resistance being in plurality for the plurality of specified periods, respectively; (ii) set a plurality of coefficients for the plurality of specified periods, the plurality of coefficients being arranged to be in ascending order from a start of the cranking period to a last thereof; and (iii) multiply each of the plurality of the local internal resistances of the battery by a corresponding one of the plurality of coefficients, and thereafter average the plurality of local internal resistances of the battery so as to calculate the internal resistance of the battery.