In the current study, the lack of generalisation to the cell population may put into question the electrochemical consistency of the cells altogether. Considering the voltage profiles of Fig. , a certain degree of cell-to-cell variation is observed. Some of this, however, has been visually exaggerated due to the uncertainty of the x-axis valuesthe charge level, Q -which experienced drift as discussed. It is reiterated that this uncertainty of the charge level is the reason our study focused on voltage rather than SoC estimation. A complementary investigation of the cell-to-cell voltage variation is provided in SI Section 3, where an additional 10 cells were cycled slowly, at a rate of C/20, to observe their quasi-OCV (qOCV) profiles. The investigation is based on constructing qOCV-versus-SoC curves for the 10 cells and overlaying them, where in this case it was possible to compute the SoC by Coulomb counting because side reactions were minimised thanks to the low C-rate. It was found that between the 10 cells, and at any SoC, the qOCV varied by a maximum of ±31 mV between 10 different cells (SI Fig. ), and by an average of ±8 mV among all SoCs. It can be concluded that this level of intrinsic cell-tocell variation does not justify the complete lack of generalisation of the machine learning regression models trained in this chapter, where mean absolute errors were higher than ±264 mV (the baseline case).