A battery gas-gauge circuit and method thereof are provided. The battery gas-gauge circuit includes a sensing resistor, a voltage-to-current conversion circuit, a subtractor, a comparator, a logic circuit and a power-management unit. In the voltage-to-current conversion circuit, two conversion circuits thereof obtain two voltage signals according to the two ends of the sensing resistor, respectively, and convert the two voltage signals to two current signals correspondingly. The subtractor generates a current difference signal according to the two current signals. The comparator outputs a comparison signal according to the current difference signal and a current dead-band. The logic circuit outputs a logic signal according to the comparison signal and a predetermined signal. The power-management unit determines battery power according to the logic signal.