Disclosed herein are a battery power supply adjusting circuit and method, a charging cable, and a terminal device. The circuit is configured to charge a dual-cell battery (010). The circuit comprises a Buck circuit module (110), a first charge pump circuit module (120), a second charge pump circuit module (130), a battery charging and discharging control module (140), and a system power supply module (150). An input of the Buck circuit module (110) and an input of the first charge pump circuit module (120) are externally connected with an AC/DC adapter (020), respectively. The first charge pump circuit module (120) and the second charge pump circuit module (130) are respectively connected to the dual-cell battery (010). The second charge pump circuit module (130) is also connected to the system power supply module (150).