Battery State Estimation

Coulomb counting integrates current over time to track charge in and out of the battery, but drifts without periodic calibration due to sensor inaccuracies or unmeasured leakage paths. It works well for relative state changes during steady-state operation but becomes unreliable after long idle periods or rapid current shifts where current measurement noise accumulates.

Open-circuit voltage relies on the battery’s resting voltage after ≥30 minutes of no load, correlating to state of charge via a lookup table—highly accurate for state of charge when the battery is relaxed. However, it cannot track dynamic changes in real time and becomes less precise in high-temperature environments or with aged cells where the OCV curve flattens.

Impedance tracking applies small AC signals at specific frequencies to infer internal resistance and estimate state of health, especially for detecting aging effects like SEI growth or lithium plating. It complements the other two by identifying degradation mechanisms but requires careful interpretation because impedance varies with temperature, state of charge, and SOC transition rates, making standalone interpretation misleading.