Charger and charging method

A charger comprising:

• a battery accommodating unit including a first contact and a second contact configured to be respectively in contact with electrode terminals of a battery accommodated therein;
• a high-potential power supply line and a low-potential power supply line to which power for charging the battery is supplied;
• a connection switching circuit capable of switching between a first connection state in which the first contact is connected to the high-potential power supply line and the second contact is connected to the low-potential power supply line and a second connection state in which the second contact is connected to the high-potential power supply line and the first contact is connected to the low-potential power supply line;
• and
• a control device for controlling the connection switching circuit to acquire a battery voltage of the battery and perform charging control on the battery,
• wherein the control device performs pre-charging on the battery in the first connection state, and when the battery voltage does not exceed a predetermined set voltage, the control device switches the first connection state to the second connection state and performs the pre-charging on the battery, but when the battery voltage exceeds the set voltage, the control device performs normal charging on the battery.