1. A method of estimating a state of charge (SOC) and a state of health (SOH) of an electrochemical cell (EC), comprising: modeling said EC with a linear equation; measuring a terminal current of said EC; measuring a terminal voltage of said EC; measuring a temperature of said EC; and processing said linear equation through a time-varying state and parameter estimator based on said terminal current, said terminal voltage and said temperature to determine states and parameters of said EC.