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