The present disclosure discloses a battery fuel gauging system, which includes a battery voltage collecting module and a microprocessor module. An input terminal of the battery voltage collecting module is configured to collect a terminal voltage of the battery. The microprocessor module is configured to receive the terminal voltage and estimate the remaining charge in the battery. The microprocessor module estimates an open-circuit voltage of the battery according to the terminal voltage of the battery and a built-in battery model, and further calculates the battery's remaining charge based on SOC-OCV relations of a typical lithium-ion battery. The present disclosure is capable of maintaining the precision of the battery fuel gauging system and can set the battery fuel gauging system inside or outside of the battery.