State of charge calibration for battery cells

A battery system comprising:

• a pressure sensor configured to sense pressure changes corresponding to thickness changes of at least one of a plurality of battery cells of a battery;
• and
• a battery management module including a state of charge (SOC) estimator configured to:
• estimate the SOC of the battery;
• based on the sensed pressure changes, detect at least one of a first inflection point and a second inflection point during one of charging and discharging of the battery;
• determine a polarity change in current to identify a transition between charging and discharging of the battery;
• and
• in response to the at least one of the first inflection point and the second inflection point being outside a predetermined period of the polarity change in current calibrate the estimated SOC of the battery based on at least one of a first SOC value and a second SOC value corresponding to the at least one of the first inflection point and the second inflection point, respectively, wherein the SOC estimator does not calibrate the estimated SOC in response to the at least one of the first inflection point and the second inflection point being within the predetermined period of the polarity change in current, and
• wherein the battery management module is configured to calculate capacity retention of the battery and to adjust the at least one of the first SOC value and the second SOC value based on the capacity retention.