Various examples of the present disclosure provide a high efficient battery backup (BBU) system and systems and methods for managing the BBU system through a microcontroller unit (MCU) and an ORing FET system of the BBU system. In some examples, a baseboard management controller (BMC) of a server system is used to control the MCU and the ORing FET system of the BBU system such that the BBU system can operate in multiple operating modes without a battery discharger. The operating modes of the BBU system includes, but are not limited to, a battery constant-current-charging mode, a battery constant-voltage-charging mode, a battery discharging mode, or a battery capacity calibration mode.