(US5672973-A)      An apparatus for monitoring residual capacity of a battery, comprising:    means for sensing a discharge current, which is supplied from a battery to a load side;    means for sensing a terminal voltage of the battery;    means for calculating residual capacity of the battery based on    (1) the terminal voltage of the battery whenever the battery has not experienced a discharge for a time period longer than a time-out period, and    (2) an approximately linear function of the terminal voltage and the discharge current whenever the battery is experiencing a discharge;    a display section for displaying the residual capacity calculated by said calculating means; and    a time-out circuit connected to the means for calculating for causing the last-calculated residual capacity to be retained for the time-out period after a discharge from the battery ceases.    (JP3164998-B2)      The measuring device consists of a current sensor (7) and a voltage sensor (9) which measures the current supplied by a main battery (3) and the voltage across it. First the current and the voltage of the main battery is measured during vehicle running. When the voltage of a sub-battery (41) is above certain value, an approximation straight line function is obtained from the terminal voltage. The residual capacity of the main battery is shown in the table, based on the approximation straight-line function.    The vehicle is stopped and the battery does not supply current. The residual capacity of the battery in no load condition is calculated. Further, a power supply control circuit prevents the ignition ON condition. The main battery voltage is stabilized after a predetermined time. The power supply voltage is brought to a level of operation of power supplied for predetermined time till the battery is stabilized.    ADVANTAGE -   Provides simple composition. Makes user to understand residual capacity of battery correctly. Displays residual capacity value with high precision.