<p>Lithium-ion batteries are an essential element for the modern age when striving for sustainable green energies, they have several advantages and are used everywhere; however, optimal monitoring and management of lithium-ion battery parameters in different conditions is still a challenging research topic. One of its key parameters is a state of charge (SoC). Although there has been a significant optimization in state-of-charge estimation methods recently, further improvements are still to be made, such as reducing computational complexity, moreover reducing the dependency on the operating conditions, This paper presents a new technique for the state-of-charge estimation that relies on combining coulomb counting as the main method, and online open-circuit voltage identification for the calibration during the charging phase. The proposed method uses a modified charging protocol by applying a predefined current pulse and based on an equivalent circuit model. To evaluate the work, a set of experiments was conducted on two different lithium-ion cells that resulted in an RMSE of 2mV for one cell, and 5.28mV for the other cell in online open-circuit voltage estimation, moreover an RMSE of 0.29%, and 0.46%, respectively, for state-of-charge estimation. This method has shown good accuracy moreover good reliability with low computational complexity.</p>