**6. Conclusions**

The infinite number of r–C chain-based equivalent circuit for a symmetric double-layer UC was evaluated in this work. The dynamic characteristics were studied to authenticate the applicability of the projected equivalent circuit in the practical working conditions. The internal resistance and capacitance values of the ultracapacitor remained relatively constant for the charging-discharging processes despite the current and voltage change in a wide range of parameters. However, the internal resistance is strongly influenced by the working temperature. The possible reason is the decay of the diffusion coefficient at lower temperatures. The EIS studies confirmed that the impedance remained constant for a wide range of applied voltage (0.3376–2.736 V) and temperatures (−30 ◦C to +30 ◦C). The reactance was determined by an inductive reactance of a connecting cable, especially for frequencies higher than 100 Hz. Following from the inductive reactance nature, the temperature did not influence it. The UC functionality, periodic, and stochastic phases of the charge-discharge current are recommended to verify using simulation software. An electrical engineer can apply the proposed equivalent circuit to estimate the electrical parameters for the development of energy storage facilities.

**Author Contributions:** Conceptualization, M.A., A.K., and A.Y.; Methodology, M.A. and S.R.; Software, M.A. and S.R.; Formal analysis, M.A., A.K., and A.Y.; Investigation, S.R.; Resources, M.A. and A.Y.; Data curation, S.R. and M.A.; Writing—original draft preparation, S.R. and M.A.; Writing—review and editing, S.R., A.K., A.Y., and M.A.; Supervision, A.Y. and M.A.; Project administration, M.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors gratefully acknowledge the support of M. Zinigrad (Ariel University), Y. Bernstein (Ariel University), and M. Perl (Wise-Tech. Co.) for the experiments. S. Rajput is thankful to the Israeli Council for Higher Education (CHE) for the fellowship.

**Conflicts of Interest:** The authors declare no conflict of interest.
