Defining An Accuracy Limit in Battery State Estimation

Batteries are everywhere in our daily lives. Their applications span from electronic devices to electric vehicles (EVs) and further to grid-scale energy storage systems. Accurate battery state of charge (SOC) and state of health (SOH) estimations are essential elements of a battery management system (BMS) that ensure the safe and efficient operation of various battery-powered equipment. SOC describes the remaining charge of the battery. It is defined as the ratio of the instantaneous remaining capacity to its present maximum capacity.1 On the other hand, SOH describes the aging status of the battery. It is defined as the ratio of the present maximum capacity to its initial maximum capacity (or nominal capacity).2 Note that SOH can also be defined by the cell’s resistance increase or power fade in some other cases.1,3 In this commentary, we will focus solely on the definition related to maximum capacity since this definition defines lifetime in most use cases.4