It should be acknowledged that a more thorough account of cell-to-cell variation would have also considered the impedimetric profiles of the cells, which affect their overvoltages at the higher C-rates used in this chapter (0.2, 0.5 and 1C). Nevertheless, the additional cell-to-cell discrepancies would need to be very large to hinder generalisation to the extent observed. A more likely explanation for the lack of generalisation is that the acoustic characteristics of the seven cells in the acoustic dataset are distinctly different, as discussed. It is also significant to consider that this distinction persists at all three C-rates -otherwise the classification scores would have been lower, and clusters in the latent spaces produced by unsupervised learning may have been less pronounced. A final consideration, with regard to sources of cell-to-cell variation, is the possibility that the dataset acquired from each cell reflects the local SoC in the tested area, rather than the global SoC measured electrochemically. However, given the small size of the cells tested (ca. 4.1 cm 2 ), spatial SoC variations are likely too minor to account for the lack of model generalisation. Additionally, the transducer used had a contact area of ca. 0.3 cm 2 , covering a significant portion of each cell (SI Section 4).