Disclosed is a method of analyzing an energy storage device including normalizing charge and discharge voltage profiles to obtain normalized charge and discharge voltage profiles as a function of a normalized capacity; averaging the normalized voltage profiles to obtain an averaged voltage profile as a function of the normalized capacity; determining an internal resistance between the charge or discharge voltage profiles and the normalized averaged voltage profile; determining a current-resistance (IR) potential responsive to a measured current and the determined internal resistance; determining an IR-free voltage charge or discharge profile of the energy storage device; and determining a ratio between a capacity change and a voltage potential change in a charging or discharging process of the energy storage device over a predetermined interval of time responsive to the determined IR-free voltage charge or discharge profiles.