State Of Charge
State of charge (SOC) is the equivalent of a fuel gauge for the battery pack in a battery electric vehicle (BEV), hybrid vehicle (HEV), or plug-in hybrid electric vehicle (PHEV). The units of SOC are percent points (0% = empty; 100% = full). SOC cannot usually be determined directly. In general there are four methods to determine SOC indirectly: This method works only with batteries that offer access to their liquid electrolyte, such as non-sealed Lead Acid batteries. The Specific Gravity or pH of the electrolyte can be used to indicate the SOC of the battery. This method converts a reading of the battery voltage to SOC, using the known discharge curve (voltage vs. SOC) of the battery. However, the voltage is more significantly affected by the battery current (due to the battery’s internal resistance) and temperature.
