How is battery State of Health (SOH) estimated in EVs?

State of Health represents remaining battery capacity or capability relative to new condition. Estimation methods include: Coulomb counting comparing full charge capacity over time, impedance measurements (increasing internal resistance indicates degradation), OCV-SOC curve analysis (shifts indicate aging), and model-based approaches using extended Kalman filters or machine learning trained on degradation data. Accurate SOH estimation enables reliable range prediction, warranty management, and residual value assessment. Challenges include variations between cells and operating conditions affecting measurements.