The impedance of a lithium battery at a single state-of-charge (SoC) is obtained from the current and voltage response of the cell. Making this measurement is important in order to understand cell characteristics. There exist some impedance analysers which can make suitable measurements at a single SoC. Measuring this impedance at multiple SoC is slow and tedious especially at lower frequencies. We present a new method which computes the impedance over a range of SoC while simultaneously varying the SoC. The proposed method produces reliable data even when the device under test is behaving non-linearly. The data obtained from this measurement is validated by comparing impedance data obtained at different SoC from a cell under no load.