A
battery capacity measuring device in accordance with the present invention has a fully-charged state
detector (80e), a detected current
integrator (80a), a divider (80b), and a corrector (80c) incorporated in a
microcomputer (80). The fully-charged state
detector detects that a battery is fully charged. The detected current
integrator integrates current values that are detected by a
current sensor during a period from the instant the battery is fully charged to the instant it is fully charged next. The divider divides the integrated value of detected current values by the length of the period. The corrector corrects a detected current using the quotient provided by the divider as an offset. Furthermore, a remaining
battery capacity calculating
system comprises a
voltage detecting unit (50), a current detecting unit (40), an index calculating unit, a
control unit, and a calculating unit. The
voltage detecting unit detects the
voltage at the terminals of a battery. The current detecting unit detects a current flowing through the battery. The index calculating unit calculates the index of polarization in the battery according to the detected current. The
control unit controls the output voltage of an
alternator so that the index of polarization will remain within a predetermined range which permits limitation of the effect of polarization on the charged state of the battery. When the index of polarization remains within the predetermined range, the calculating unit calculates the remaining capacity of the battery according to the
terminal voltage of the battery, that is, the open-circuit voltage of the battery.