This paper provides the results of impedance measurements on commercially available LiCoO 2 | C coin-type cells. The impedance response was shown to be extremely sensitive to state-of-charge, overcharge, and over-discharge. Interestingly, the impedance showed a persistent change to the electrochemical characteristics of a coin cell subject to overcharge; whereas, the electrochemical characteristics returned to normal for a coin cell subject to over-discharge. A measurement model analysis was used to show the reversibility of the impedance behavior of an over-discharged cell and the irreversibility of the impedance response of an overcharged cell.