Rechargeable battery device, and power supplying system incorporating the same

A power supplying system (10) includes multiple rechargeable battery devices (2) each including a first switch module (21), a series connection of a battery unit (22) which includes multiple rechargeable batteries connected in series with each other and a second switch module (23) connected in parallel to the first switch module (21), and a control module (24) for controlling operations of the first and second switch modules (21, 23). For each rechargeable battery device (2), the first and second switch modules (21, 23) are normally operated in an OFF-state and an ON-state, respectively, and the control module (24) enables the first and second switch modules (21, 23) to switch respectively from the OFF-state and the ON-state to an ON-state and an OFF-state upon detecting that a voltage of any one of the rechargeable batteries of the battery unit (22) is not within a predetermined voltage range during charging or discharging of the battery unit (22).