A battery unit for a flavor inhaler, comprising: a chargeable and dischargeable power supply; a connection part capable of electrically connecting to an external charger; a controller configured to perform control regarding at least the power supply; and a switch configured to allow an electrical connection and disconnection between the external charger and the power supply, wherein the controller is configured to: detect whether the charger is connected to the connection part; while the charger is connected to the connection part, cause the switch to alternate between an electrical connection and disconnection of the power supply to the connection part, such that the electrical disconnection is carried out in response to a first predetermined time period elapsed since the electrical connection has established, and thereafter the electrical connection is carried out in response to a second predetermined time period being elapsed, thereby periodically stopping charging to the power supply from the charger; measure an accumulated value of a connection time period to the charger without including a period during which charging is periodically stopped, wherein the accumulated value of the connection time period to the charger is counted while the switch is in a connection state; and determine whether the accumulated value of the connection time period to the charger exceeds a first predetermined time period to identify that the power supply has been degraded. a chargeable and dischargeable power supply; a connection part capable of electrically connecting to an external charger; a controller configured to perform control regarding at least the power supply; and a switch configured to allow an electrical connection and disconnection between the external charger and the power supply, wherein the controller is configured to: detect whether the charger is connected to the connection part; while the charger is connected to the connection part, cause the switch to alternate between an electrical connection and disconnection of the power supply to the connection part, such that the electrical disconnection is carried out in response to a first predetermined time period elapsed since the electrical connection has established, and thereafter the electrical connection is carried out in response to a second predetermined time period being elapsed, thereby periodically stopping charging to the power supply from the charger; measure an accumulated value of a connection time period to the charger without including a period during which charging is periodically stopped, wherein the accumulated value of the connection time period to the charger is counted while the switch is in a connection state; and determine whether the accumulated value of the connection time period to the charger exceeds a first predetermined time period to identify that the power supply has been degraded. detect whether the charger is connected to the connection part; while the charger is connected to the connection part, cause the switch to alternate between an electrical connection and disconnection of the power supply to the connection part, such that the electrical disconnection is carried out in response to a first predetermined time period elapsed since the electrical connection has established, and thereafter the electrical connection is carried out in response to a second predetermined time period being elapsed, thereby periodically stopping charging to the power supply from the charger; measure an accumulated value of a connection time period to the charger without including a period during which charging is periodically stopped, wherein the accumulated value of the connection time period to the charger is counted while the switch is in a connection state; and determine whether the accumulated value of the connection time period to the charger exceeds a first predetermined time period to identify that the power supply has been degraded.