The nissan leaf demonstrated this problem in Phoenix immediately upon release, it is a known thing. Tesla seems to take yhe cooling loop very seriously. The batteries in the early model s had some issues but after that they seem to asymptote at 20% range loss and stay there. At least so far. I don't know who else takes cooling that seriously. I'd look for liquid cooling but also phase change hooked into the ac system, as liquid and a radiator only gets you down to ambient, which is too hot in an increasingly large number of locations much of the year.
Yep, our i3 battery is cooled as a pack, but degraded fast north of Phoenix (higher altitude, still hot as hell for 4 months, super nice for 8 months including freezing and occasional snow). Turned out the cooling system for the original pack broke, but it was unclear if that happened in Arizona or was a one-off quirk, so the degradation of the original pack happened for sure in Arizona.
