Measuring internal impedance before use is a good way to identify cells that may be at risk of failure. One technique is electrochemical impedance. The internal resistance is the key parameter for determining power, energy efficiency and lost heat of a lithium ion cell. Precise knowledge of this value is vital for designing battery systems for automotive applications. Internal resistance of a cell was determined by current step methods, AC. Electrochemical impedance spectroscopy (EIS) analyzes electrochemical systems by measuring impedance over frequencies to assess charge transfer, mass transport, and interfacial capacitance.