A voltage control apparatus checks a battery voltage when an automotive generator gradually increases its output to be within a predetermined range after temporarily stopping the generator. Then, the battery voltage is picked up to calculate the charge rate. Further, a first charge rate and a first residual capacity of the battery is memorized when the engine is stopped. Periodically, a pseudo-open circuit voltage is checked when a charge/discharge current fits within a predetermined small range while the engine is not running, and a second charge rate calculated based on the checked pseudo-open circuit voltage. A second residual capacity is calculated using the first charge rate, the first residual capacity and the second charge rate.