NOVELTY - The method involves determining a terminal voltage of battery cell during equilibrium condition and a charge current of battery cell during charging operation. The capacity to store lithium ions of positive electrode (124) and negative electrode (120), and the total amount of lithium ions in battery cell are estimated based on a model relating state of charge of negative electrode and average open circuit potential of positive and negative electrodes. An output corresponding to the estimate of storage capacity of lithium ions and the total amount of lithium ions are generated.    USE - Method for estimating parameter of lithium-ion battery cell in lithium-ion battery system (claimed) for portable electronics and electric and hybrid-electric vehicles.    ADVANTAGE - The capacity of a lithium-ion battery system is estimated effectively in a simplified manner.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for lithium-ion battery system. The parameter estimation technique is one of nonlinear-least squares, nonlinear Luenberger observer design, and extended Kalman filter. The state of charge of the negative electrode of the battery cell is determined according to discretized model, and the state of charge of the negative electrode is determined according to an optimization problem approach. The state of the discretized model in real-time is estimated using an observer design technique. The optimization problem approach includes a batch optimization and a recursion-based optimization. The positive and negative electrodes include active materials that store lithium ions. A voltage sensor generates a voltage signal representative of a voltage between the positive electrode and the negative electrode during an equilibrium condition of the lithium-ion battery cell. A current sensor generates a current signal representative of a current associated with the lithium-ion battery cell. A processor executes the command instructions to use a parameter estimation technique to estimate the capacity to store lithium ions of positive and negative electrode, and a total amount of lithium ions in battery cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a battery system.    Lithium-ion battery system (100)    Memory (112)    Processor (116)    Negative electrode (120)    Positive electrode (124)