Abstract: A new definition method to describe the state of the batteries in a hybrid-electric-vehicle (HEV) was proposed. The batteries in the question are MH/Ni batteries which have a normal capacity of about 8 A·h, and were used in a kind of HEV. The HEV application is a very harsh environment with high charge or discharge rates and very dynamic rate profiles. The normal definition method state of charge (SOC) that worked well in benign portable electronic applications may not work well in the HEV application. The normal definition of SOC cannot contain both the static and the dynamic message of the batteries in the only word. In the new definition method, the static state of charge (SSOC) and the dynamic state of charge (DSOC) were proposed. The SSOC indicates the static capacity message of the batteries; the DSOC indicates the dynamic state of charge while charging or discharging. The methods of how to calculate the SSOC and the DSOC were discussed.