Plus they do the battery pack design, construction and software themselves. That includes testing of what temperature, power draw and charging regimes cause deg

Plus they do the battery pack design, construction and software themselves. That includes testing of what temperature, power draw and charging regimes cause degradation, how to keep the cells within a good regime while maintaining performance, when to cheat, how to prevent fires and so on. You don’t just put 7000 cells in parallel and call it a day. (Well, some manufacturers do, but the results vary).