State of Charge (SoC) is a parameter used to determine the current capacity on a battery as well as indicate the operational characteristics. The SoC is an important parameter for optimizing battery utilization in many applications requiring DC current source. However, estimating the SoC value is the major problem since it cannot be measured directly. In this study, we proposed SoC measurement method based on analysis internal resistance of battery. The internal resistance is correlated with the parameters of the magnitude of the terminal voltage and open circuit. Both voltages come from the influence of current during the charging-discharging process. We report that the proposed method has successfully obtained the correlation between the SoC and the internal resistance value for two process, which are the charging- and discharging process. © 2022 International Energy Journal. All rights reserved.