5 Challenges Modeling Battery Response to Dynamic Load Currents

The resistor and capacitor battery model captures significant aspects of the battery behavior versus age and load current level using a simple equivalent circuit. The equivalent circuit captures the battery behavior well when load currents are stable, and transient voltage responses settle. In practice, batteries exhibit voltage transient responses with significant duration in response to changes in load current.

Figure 5-1 Battery Transient Response

As seen in Figure 5-1, the battery voltage transient can require more than 10 minutes to settle in response to a C/2 step in load current. After the relaxation time has passed, the resistor and capacitor battery model generates an accurate prediction of the battery terminal voltage. After the relaxation time, the battery resistance model can be updated accurately since the difference between OCV and battery terminal voltage is equal to the IR drop predicted by the model. Traditional gauge algorithms, such as the Impedance Track algorithm, do not update the resistance model unless the load current is stable enough for this settling to occur.