The participants were asked to calculate a range of electrochemical parameters from the provided datasets including total capacitance (F), specific capacitance (F g -1 ), and total internal resistance (Ω). The analysis requested from each dataset is summarised in Figure . All results received have been anonymised and randomised in the Results and Discussion section below. A full list of the reported results is shown in the Supplementary Information (SI Section 4). It is important to note that not all participating groups supplied data for each data file. For Files 1 -4, only data from cycle 3 is presented in the Results and Discussion section for simplicity. All cycles showed the same trends.