I'm not positive on the specifics but I believe it has more to do with the combination of supported voltages/amperages offered by different chargers. i.e. a "350 kW capable" charger in practice means it can do 800V charging, which other chargers of lower kW ratings typically can't do, and the EV6 requires 800V to reach its max charge speed but can't actually handle a high enough amperage to get to 350 kW.
Like I said though, I might be confused on some of the details there, but I'm fairly positive it's not just waste heat...dissipating 110kW of waste heat would require some pretty insane cooling hardware.
Oh, and EVs presumably vary wildly in their "fuel economy" (miles per kilowatt-hour or whatever unit EV folks use), so even a "fair" comparison of charging rate presumably wouldn't paint the entire picture.
This is indeed a good point. A more relevant measure of charging speed would be something like "miles per hour at EPA rated efficiency", though even that gets messy since most cars don't charge at a linear speed. And I haven't seen any car manufacturers use this metric other than Tesla, who like to brag about their supercharger stations exceeding 1,000 MPH of charging speed (though only the newest stations can just barely do that, for very short durations, and only on certain car models). "Time from 20%-80% charge" would also be a better metric, due to non-linear charging speed curves, but I haven't seen that one used much either.
Pretty much the only time charging speed even matters is the "road trip" mode, where you are driving further than a single battery charge in one day and you want to stop as little as possible. In that mode, all I really want to know is what my duty cycle will be, e.g. "every 5 hours of driving you'll need to stop to charge for 30 minutes."
If I'm not in road trip mode, then as long as I can Level 2 charge overnight and/or all day at work, I would barely care what the peak charge rate is. It would still be nice to have something quick for the rare pickle (and of course road trips), but it doesn't seem like that big of a deal. I guess it's so prominent in marketing because range anxiety is still so deep in our mindset?
> it's really frustrating how hard it is to compare charge speed from different manufacturers
Is the discrepancy just the inefficiency (i.e. waste heat) of the charging circuitry and/or battery chemistry? And if so, do different EV battery+charger systems have significantly different efficiencies?
I would have expected that the consumer-facing spec is always the power taken from the grid, that there is always some inefficiency (you can draw less energy from the batteries than came out of the grid), and that the level of efficiency would be roughly similar across all cars.
If that were the case, it wouldn't be much of a problem to compare charging rates across cars. But perhaps one or more of my expectations are wrong.
Oh, and EVs presumably vary wildly in their "fuel economy" (miles per kilowatt-hour or whatever unit EV folks use), so even a "fair" comparison of charging rate presumably wouldn't paint the entire picture.