I. Introduction
State of charge (SOC), The State of charge of a battery is its available capacity expressed as a percentage of its rated capacity. The users can estimate the life of the battery and know when the batteries need to be recharged or changed through the data of SOC. It is one of the important parameters during the use of the battery. Therefore, prediction of the state of charge of battery has becomes a pivotal part of battery management. At present, several methods of estimating the state of charge of a battery have been used. Some are specific to particular cell chemistries. Most depend on measuring some convenient parameter which varies with the state of charge. Such as: open circuit voltage law, Ah measurement, internal resistance method and so on. And some intelligent forecasting methods which are combined with smart arithmetic, but there are certain shortcomings.