I am trying to simulate the thermal behaviour of a custom 6S4P cylindrical Li-ion battery pack (21700 cells) under 1C continuous discharge (~20A total, 45°C ambient). The goal is to identify hot spots within the cell array and evaluate whether a passive aluminium heat spreader between cell rows is sufficient to maintain all cells below 50°C. My current setup: - Geometry: simplified cylindrical cell bodies arranged in a 6×4 array with an aluminium spreader plate between each row, modelled in CAD and imported as a STEP file. - Physics: I am using the Conjugate Heat Transfer (CHT) solver in SimScale. - Heat source: This is where I am stuck — I am unsure how to correctly assign volumetric heat generation (W/m³) per cell based on a known IR of ~15 mΩ per cell and 5A per cell at 1C. My specific questions: 1. Is Q = I²R the right basis for volumetric heat input per cell, or should I also account for entropic heat from the electrochemical reaction at this discharge rate? 2. How do I assign different heat generation values to individual cells within a grouped solid body in SimScale — is this done via material assignments or a custom boundary condition? 3. Has anyone validated a passive-cooled cylindrical cell pack CHT model against measured temperatures? I want to understand what level of geometry simplification (e.g. ignoring the jellyroll internal structure) is acceptable before results become unreliable. I have gone through the SimScale battery thermal tutorial but it covers pouch cells with uniform heat load — my case involves cylindrical geometry and non-uniform IR across the pack. Any guidance appreciated.