This research introduces different graphical estimation methods for modeling energy storage systems using Equivalent Circuit Models (ECMs) derived from Electrochemical Impedance Spectroscopy (EIS) data. As an initial case study, the approach was applied to Lithium-ion Capacitors (LiCs) that combine the high energy density of lithium-ion batteries with the high power density of supercapacitors and require advanced modeling techniques to capture frequency dependent behaviors. This study compares three ECM configurations: the Simple Pore model including a Constant Phase Element (SP-CPE),the CPE in series with R||CPE model, and the SP-CPE in series with R||CPE model. It also introduces a fourth model: SP-CPE in series with two R||CPE branches. Each model is evaluated at different States of Charge (SoC). While the initial models only performed well at low frequency ranges and for high SoC values, the SP-CPE model with dual R||CPE branches accomplished precise results for all frequency ranges at low SoC results. The newly developed model’s accuracy relies on the extraction of parameters

from the dual semicircle behavior in the impedance plots; thus, it faces limitations due to the instability in semicircle behavior at high SoC. This work lays ground for future improvements to deliver a model capable of capturing complex LiC behavior across different SoC values.