Caps can withstand thermal cycling much better than batteries and their operating temp is between -40-70degC.
So can titanate cells (not quite 70°C, but still hot). And while they're far more expensive than Tesla's cells, they're still vastly cheaper than supercapacitors. Much less energy density than Tesla's cells, but orders of magnitude more than supercapacitors. They don't leak like supercapacitors. Huge cycle life. Power density of several kilowatts per kilogram (I know that even a decade ago there were manufacturers offering cells that did 5kW/kg).
Supercapacitors are just a nonstarter. If Tesla wanted more power, they'd just use higher-power li-ions. But even that tradeoff isn't worthwhile.
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