Why is battery characterization required?

The electrical parameters of the Thevenin Battery Model are not fixed values. Instead, they depend on the characteristics of the battery and vary with operating conditions. As a result, the parameters required by the model cannot be selected from generic values and must be determined experimentally.

Several factors influence battery behaviour, including:

• State of Charge (SoC)
• Temperature
• Battery chemistry
• Cell aging and degradation

These factors affect the battery's voltage response, internal resistance, and polarization behaviour. Consequently, two batteries of different chemistries or different ages may exhibit significantly different electrical characteristics even when operated under the same conditions.

Battery characterization is the process of measuring the electrical response of a battery under controlled conditions to obtain the experimental data required for modelling. The resulting datasets describe how the battery behaves over its operating range and provide the foundation for identifying the parameters of the Thevenin model.

Two characterization tests are commonly performed for Equivalent Circuit Models:

• Open Circuit Voltage (OCV) test, which measures the equilibrium voltage of the battery at different States of Charge.
• Hybrid Pulse Power Characterization (HPPC) test, which measures the battery's dynamic voltage response during current pulses.

Together, these tests provide the experimental data required to construct an accurate battery model suitable for simulation and State of Charge estimation.

The following section introduces the Open Circuit Voltage test and explains how the relationship between Open Circuit Voltage and State of Charge is obtained.