State-of-charge (SOC) estimation becomes an increasingly important issue in all the applications that include a battery. Former operation strategies made use of voltage limits only to protect the battery against deep discharge and overcharge. Currently, battery operation is changing to what could rather be called battery management than simply protection. For this improved battery control, the SOC of Battery is a key factor. Many research works has been done in recent years to improve SOC estimation. Operational conditions differ for batteries in, for example, photovoltaic applications, (hybrid)-electric vehicles or telecommunications. Hence, a given method for SOC calculation will be more suitable for a certain application than for another. The authors introduce simple hybrid methods for SOC estimation. It is more suitable for HEV application.