A battery pack, comprising: a battery comprising a secondary battery; a notification unit (31, 35) configured to notify that the battery is in a fully charged state; a determination unit configured to determine whether the battery is in the fully charged state; a processing unit configured to execute a full charge process if it is determined by the determination unit that the battery is in the fully charged state, the full charge process being one of causing the notification unit (31, 35) to make a notification and maintaining a possible state, in which making a notification by the notification unit (31, 35) is possible; and a factor detection unit configured to detect occurrence of at least one predetermined increase factor during execution of the full charge process, the at least one predetermined increase factor leading to an increase in a chargeable capacity of the battery as compared with the time when it is determined by the determination unit that the battery is in the fully charged state, wherein the processing unit is configured to stop the full charge process if occurrence of the at least one predetermined increase factor is detected by the factor detection unit during the execution of the full charge process, wherein the battery pack is attachable/detachable to/from a main body of a motor-driven appliance, and allows discharge from the battery to the main body while being attached to the main body, wherein the battery pack includes a discharge detection unit configured to directly or indirectly detect that a discharge from the battery to the main body is performed, wherein at least one of the at least one predetermined increase factor is a detection of the discharge by the discharge detection unit, wherein the main body includes an operation switch to be operated to perform a discharge from the battery to the main body, and is configured to transmit, when the operation switch is operated, an operation signal indicating the fact of operation to the battery pack, and wherein the discharge detection unit is configured to detect, when receiving the operation signal from the main body, that a discharge from the battery to the main body is performed. a battery comprising a secondary battery; a notification unit (31, 35) configured to notify that the battery is in a fully charged state; a determination unit configured to determine whether the battery is in the fully charged state; a processing unit configured to execute a full charge process if it is determined by the determination unit that the battery is in the fully charged state, the full charge process being one of causing the notification unit (31, 35) to make a notification and maintaining a possible state, in which making a notification by the notification unit (31, 35) is possible; and a factor detection unit configured to detect occurrence of at least one predetermined increase factor during execution of the full charge process, the at least one predetermined increase factor leading to an increase in a chargeable capacity of the battery as compared with the time when it is determined by the determination unit that the battery is in the fully charged state, wherein the processing unit is configured to stop the full charge process if occurrence of the at least one predetermined increase factor is detected by the factor detection unit during the execution of the full charge process, wherein the battery pack is attachable/detachable to/from a main body of a motor-driven appliance, and allows discharge from the battery to the main body while being attached to the main body, wherein the battery pack includes a discharge detection unit configured to directly or indirectly detect that a discharge from the battery to the main body is performed, wherein at least one of the at least one predetermined increase factor is a detection of the discharge by the discharge detection unit, wherein the main body includes an operation switch to be operated to perform a discharge from the battery to the main body, and is configured to transmit, when the operation switch is operated, an operation signal indicating the fact of operation to the battery pack, and wherein the discharge detection unit is configured to detect, when receiving the operation signal from the main body, that a discharge from the battery to the main body is performed.