Abstract: Systems and methods are disclosed for estimating state parameters of lithium manganese iron phosphate (LMFP) battery cells with improved accuracy and robustness. Per-cell estimation of state of charge (SOC) and state of health (SOH) is performed using electrical measurements including voltage, current, and temperature. In example implementations, shifts in characteristic voltage transition regions associated with manganese- and iron-based redox reactions are monitored to infer degradation during normal operation. Mechanical swelling force of the battery cell is measured using one or more pressure sensors, providing a physical indicator correlated with SOC and long-term lithium inventory loss, particularly in voltage-flat operating regions. Direct current internal resistance values obtained from controlled current pulses may further enhance estimation accuracy.