Open Cell Voltage - DC
Voltage is function of SOC
The voltage across positive and negative terminal of battery while not discharging current to a load
The internal resistance of the battery causes the OCV to decrease when current is discharged from it.
Open Cell Voltage - AC
Voltage is function of SOC
In this model, R0 is internal resistance, R1 & C1 model the short term transient response, and R2 & C2 model the long term transient response.
Table Lookup
The table relates capacity to voltage, current, temperature, and age.
Not practical takes time to collect and test data
Does not require a cell model
Voltage Lookup
Accurate voltage measurements can be made while a cell is resting
The relation between capacity and voltage is non-linear. A typical model is shown below
Coulomb Counting
Involves counting the charges going into the battery by integrating the current
Requires knowledge of the initial amount of charges
Defining Q as the total capacity of the battery in Ah/mAh leaves us with the following equation sets of equations
Factors that Affect Capacity Estimation
PCB component accuracy
Instrumentation accuracy
Cell model accuracy
Aging
Temperature