This circuit note describes an electrochemical impedance spectroscopy (EIS) measurement system for characterizing lithium ion (Li-Ion) and other types of batteries. EIS is a safe perturbation technique used to examine processes occurring inside electrochemical systems. The system measures the impedance of a battery cell over a range of frequencies. The data can determine the state of health (SOH) and state of charge (SOC) of a battery. Using an ultralow power analog front end (AFE), this system is designed to excite and measure current, voltage, or impedance response of a battery.