So I got a record number of disagrees regarding my comment about Tesla potentially announcing on the "Battery Investor Day" a decision to not use cylindrical cells and migrate to 'flat' cells such as pouch or prismatic cells. At the risk of this being OT (although it IMHO matters directly to Tesla investments, cost of goods and cell manufacturing capex and ramp-up speed), here's how I see it: Actually, this is a common misconception, cylindrical cells are pretty much the worst-case layout for heat management, because the available heat flux from the innermost 'core' layers dictates the overall cooling requirements - and those layers are a comparatively smaller fraction of the total mass: To get the heat of those innermost layers out of the cell they external surface of the cell has to be cooled more than an equivalent flat cell would have to be, because the heat as to be disspitated through more layers which are all heat generating as well. With prismatic, pouch and other types of 'flat' cell designs the mass-to-surface ratio and thus the potential cooling surface is much larger and the size of the innermost limiting layer is similar to the other layers: I.e. the same chemistry and same mass can be cooled more effectively and more uniformly in flat cells than in cylindrical cells - and the volume can be kept at a more uniform temperature as well. This is a result of the basic geometry of their layout. Flat cells can also be packed more effectively, as there's no volume loss due to the circle packing loss of cylindrical cells: Note how wasteful cylindrical cell packing is, compared to flat cells. Plus the cooling channels only touch part of the surface of the cylindrical cells: Note how in that tear-down image the cooling channels are touching maybe 30% of the circumference of each cell. Cylindrical cells also complicate pack design due to their very granular and not easy to pack nature. I don't think it's an accident that the big Model 3 delay was related to the ... unexpectedly low performance of cylindrical cell based battery pack assembly lines. Contrast this with the heating and packing efficiency of whole-surface two side contact flat cells. I believe Tesla's cars have superior charging speeds not because of cylindrical cells, but despite using cylindrical cells. Whether the better cooling of flat cells, combined with their better volumetric density, matters enough for Tesla to go through the trouble of switching form factors, I have no idea - but I don't think it's nearly as obvious as you appear to make it.