Charging circuit

A charging circuit, comprising:

• a power source circuit that supplies charging power to multiple secondary batteries;
• a switch that controls the supply of the charging power from the power source circuit to the multiple secondary batteries;
• and
• a control device that performs switching control of the switch based on respective voltage values of the multiple secondary batteries,
• wherein:
• the control device detects a voltage difference among the multiple secondary batteries before starting charging;
• the control device starts a timer for setting an upper limit of a total charging time, and starts serial charging of the multiple secondary batteries;
• in a condition that the voltage difference among the multiple secondary batteries before the charging is equal to or larger than a first threshold, if the respective voltage values of the multiple secondary batteries all become equal to or larger than a second threshold before the timer expires, the control device shortens a remaining time on the timer at that time point;
• and
• the control device finishes the serial charging of the multiple secondary batteries at the earlier of a time point when the multiple secondary batteries have all become fully charged, or a time point when the timer has expired.