A new electrochemical instrument is described that permits the rapid and precise measurement of electrode parameters of reaction. The described techniques, previously called electrochemical potential spectroscopy, are particularly valuable in studying solid‐state reactions and phase transitions and are generally useful whenever approximations to equilibrium data are required on slow processes. The instrument may also be viewed as a general purpose instrument for measurement of electrical capacitance. It automatically measures the voltage–composition– current–time relations on an electrochemical cell by systematically stepping the voltage through a series of programmed constant voltage steps. The instrument is designed for three‐electrode measurements and has been fully developed and tested on a large number of electrochemical systems. Three commercial lithium cells are measured to illustrate the method, its time saving advantages, and its weaknesses. Comparison is also made to open circuit data collected on Li–V2O5. Three electrode measurements are reported elsewhere.