Publications in the field on Lithium Batteries and their BMS (Battery Management System).
The BMS state of health (SOH) valueMost battery packs have a BMS that is based on a standard IC solution. Well known suppliers are O2micro and Texas Instruments. They have documented to algorithm used to calculate the State of Health. The chips computer the FullChargeCapacity (FCC) value if a discharge from full to empty has been done.