Method and system for estimating the charge level of a lithium electrochemical element including a lithium phosphate positive electrode

The method involves measuring voltage of an electrochemical element (E11). Adjusted charge state of the element is determined when value determined from a calibration relationship of voltage as a function of charge state is assigned to the adjusted state and zero value is assigned to a parameter corresponding to cumulative error in charge state obtained by coulometry, or coulometry determined value is assigned to the adjusted state. Cumulative measurement error for measurement of the charge state between time periods is determined. Independent claims are also included for the following: (1) a system for estimating charge state of an electrochemical element (2) an estimation system assembly (3) a computer program product having a set of instructions for estimating charge state of an electrochemical element (4) a computer-readable data carrier having a set of instructions for estimating charge state of an electrochemical element.