Abstract: A battery pack includes a rechargeable battery, a charge FET including a parallel diode connected in series with the battery, and a control circuit configured to control turning on and off of the charge FET. The control circuit includes a discriminating circuit configured to detect a bicycle-mounted state and a charger-connected state, and a memory configured to store a full charge voltage of the battery. The control circuit is configured to, while the discriminating circuit detects the bicycle-mounted state. turn off the charge FET. The control circuit is configured to, while the discriminating circuit detects the charger-connected state, stop charging the battery by switching the charge FET to turn off the charge FET upon detecting that a voltage of the battery charged by a charger becomes higher than the full charge voltage.