Charging rate calculation system

Outputting a first estimated charging rate based on the estimated open-circuit voltage of the secondary battery, the second based on the measured current and the error limit of the secondary battery in the battery capacity of the integration result and the secondary battery at a predetermined period and outputs an estimated charging rate, the measured current and the error limit value of the third estimated charge rate and output based on the result and the battery capacity obtained by integrating a predetermined period, and the integration result and the battery capacity measured current at a predetermined cycle outputting a fourth estimated charge rate based on. Within a period of a predetermined period and outputs the fourth estimated charge rate as the charge rate, at the end of a predetermined period, the first estimated charge rate is estimated charge rate between the second estimated charge rate and the third estimated charge rate values a first estimated charging rate and the charging rate when it is, when the first estimated charge ratio is equal to or greater than the second estimated charge rate has a charging rate of the second estimated charge rate, the first estimated charging rate third when the value of the following estimated charge rate to charge ratio of the third estimated charge rate.