This section describes the data obtained with the procedure outlined above for measuring the electrolytes density and viscosity, while varying the State of Charge, SoC, total vanadium concentration, c V , and sulphates concentration, c S . We prepared four sample groups with c V = (1.830, 1.525, 1.220, 0.915) M while keeping c S = 4.07 M constant. In addition, we prepared three additional groups with c S = (3.40, 2.80, 2.20) M and c V = 0.915 M constant. For each sample group, we prepared six dilutions varying the SoC = (0, 0.2, 0.4, 0.6, 0.8, 1). The density and viscosity of these samples were measured at three temperatures T = (10, 20, 30) • C. Furthermore, we added 10 randomised samples with arbitrary values of the four parameters chosen within their respective evaluated range. The measurement points, with their respective parameter values and density and viscosity measurements, were collected in a separate csv format file that is freely available as indicated in the data availability section. It is important to note that in the main sample groups we varied only c V while keeping c S constant, or vice versa. This prevented the observation of the effect of simultaneous changes in both c V and c S . The random samples enabled us to capture the collective influence of all parameters at once, therefore improving the precision of the fit. Accounting for the posolyte and negolyte, the number of samples doubled to a total of 272 measurement points.