A battery fuel gauge circuit for determining the state of charge of a rechargeable battery is presented. The circuit comprises: a coulomb counter for providing values that are indicative of a charging current or discharge current provided to/by the battery; a voltage sensor; a first pre-processing unit to provide a current change estimate based on the values provided by the coulomb counter; an event filter unit to confirm whether the current change estimate exceeds a certain threshold; an electromotive force unit to determine an electromotive force value of the battery; a state of charge estimator unit to determine the state of charge of the battery based on the electromotive force value.