The battery pack includes: a charging terminal receiving power from a charger while connected to the charger; a battery connected to the charging terminal and recharged by power from the charger via the charging terminal; a protective circuit performing a protective operation of detecting an overcharge of the battery by using power from the battery while receiving a driving signal, and terminating the protective operation when receiving no driving signal; an activation terminal receiving an activation signal from the charger while connected to the charger; an activation circuit connected to the activation terminal and configured to output the driving signal to the protective circuit while receiving the activation signal from the charger via the activation terminal; and an auxiliary activation circuit connected to the charging terminal and configured to provide the driving signal to the protective circuit while the battery receives power from the charger via the charging terminal.