Abstract-Automotive Industry is growing at a very fast rate. Hence problems pertaining to the increasing CO2 levels in the atmosphere and the ever increasing fuel rates also increase. Electric and Hybrid electric technology has become the latest milestone for the automotive industry. In Hybrid Electric Vehicles (HEV), the reliable range of operation is characterized by batteries and battery state of charge (SOC), that describes its remaining capacity, is an important factor for providing the control strategy for the battery management system (BMS) in plug-in hybrid electric vehicles (PHEV) and electric vehicles (EV). Accuracy in estimation of the SOC is necessary not only to protect the battery, prevent it's over discharge, and improve the battery life but also to allow the application to make rational control strategies to save energy. However, the chemical energy of a battery which is a chemical energy storage source cannot be directly accessed and this issue makes the estimation of the SOC of a battery difficult. Hence, estimation of the SOC accurately becomes very complex and is difficult to implement, as there are parametric uncertainties and the battery models are limited. In fact, in practice several examples of models of the estimation of the SOC are found which have poor accuracy and reliability. Hence a comparative study done in this paper on the various methods will help choose the right method based on the requirements and the application. This paper also reviews a case study on modeling and simulation of one of the methods of SOC estimation and efforts have been put in obtaining the performance of Li-ion batteries by calculating the SOC using Coulomb counting method in MATLAB Simulink. Keywords-State