State of Charge (SoC) is the most important parameter to be estimated on a Battery Management System (BMS). Improper SoC management can cause faster battery degradation, reduce its operational lifetime and, on extreme cases of overcharge, it may lead to an explosion. In addition, batteries are complex electrochemical systems, and both the electrical components and chemical reactions vary significantly with changes in temperature. In this paper, it is presented the effect of the temperature on the Lead Acid battery SoC estimation. The data collection was performed varying the battery temperature, under a range of 10oC to 70oC. To determine the model parameters from the used battery, several data acquisition was performed. To obtain the SoC estimation it was implemented the Extended Kalman Filter that provide satisfactory results. The simulated results were obtained using the MATLAB environment. To verify the effectiveness and the performance of the implemented Kalman Filter it was applied the EKF for estimate the SoC of a Lead Acid battery described in the Introduction Section. It is important to realize that is a comparative study and the only evaluation comparison with the SoC estimation that we can do uses the Open Circuit Voltage (OCV).