There are several sources of heat generation in batteries. The irreversible and reversible heat components are considered important as the active materials' dominating heat generation. For high C-rates (most scenarios) more than half of the heat generation can be ascribed to irreversible heat, known as ohmic heat loss. At low C-rates (1C or less) the reversible heat contribution from the material phase changes becomes more significant, this heat generation is due to the entropy changes that occur as a result of intercalation reactions, and this property depends on the internal temperature and OCV of the system. The entropy change can account for over half the total heat generated at the rates typically used in electric vehicles. Parameterisations that outline activation energies do not characterise the reversible heat of the battery, this is important to predict temperature and the influenced electrochemical performance correctly. The change in entropy ∆𝐹𝐹 can be determined through the slope of the OCV with temperature: 72