Determining battery DC impedance

A method and apparatus for measuring battery cell DC impedance by controlling charging of the battery cell. The method includes real-time characterization of a battery, (a) measuring periodically a DC impedance of the battery to determine a measured DC impedance; (b) ratioing the measured DC impedance to a reference DC impedance for the battery to establish an impedance degradation factor; (c) obtaining, during use of the battery and responsive to a set of attributes of the battery, an operational reference impedance for the battery; and (d) applying the impedance degradation factor to the operational reference impedance to obtain a real-time effective impedance for the battery.