Li-ion batteries are evermore present in the modern world. Proper modeling of these batteries’ behavior involves the calculation of certain parameters from experimental test data. The objective of this article is to illustrate how certain parameterization methods can lead to differences in the resulting parameters, in terms of coherence and reliability. In this paper, a set of experimental results of LFP battery cell is considered. The cells were tested at different temperatures, depths of discharge and current values. Different curve fitting approaches will be compared for calculating the parameters of an electrical equivalent circuit model. We show that certain choices of fitting can pollute the obtained parameters, adding a variability that does not necessarily come from the experimental tests.