A total of seven commercial cells with a nominal capacity of 210 mAh and LiCoO 2 /Gr chemistry (Model 651628, AA Portable Power) were used. A complete specification sheet is provided in the Supplementary Information (SI). The same cell was used in some of the aforementioned acoustic studies , including Davies et al. who claim a generalised state estimator. Cycling was performed with a computer-controlled potentiostat (Interface 1010E, Gamry instruments, US). The surface temperature was monitored with an N-type thermocouple, attached to the surface of cells using polyamide adhesive tape, and using a TC-08 thermocouple interface (Pico Technology, UK). Tests were conducted on a bench top and the ambient temperature varied according to laboratory conditions. All cycling was performed between the manufacturer's stated voltage limits of 2.75 and 4.2 V.