I heard something today that makes me very skeptical. A dealership claimed that charging an EV with 11 kW has higher energy efficiency than charging with 6 kW. (And they didn’t mean 3-phase vs. 1-phase!)
Even if it is somehow related to battery temperature and receptiveness, that would still be heat loss. With higher currents, resistance increases, too, no? Or is it proportional and always the same percentage?
In any case, I find it foolish to follow such advice because there are other factors involved, mainly a battery suffering more regarding longevity if charged faster, and that is a lot more expensive of a loss, eventually, also because an older battery is generally less efficient in several ways. (internal resistance, self-discharge)
Plus more load spike on the grid, external and house. But I don’t want to rant too much about the lack of reason in the world that seems to be a self-amplifying spiral of doom. Apparently house charger impatience is a thing. Three hours of charging twice a month - absolutely intolerable to some.
As a first cut, power loss in the charger goes as I^2 R, where I is the current and R is the wire resistance.
The wire resistance is not a function of current in general. The power the battery gets is IV, where I is the current and V is the voltage.
For a given charging rate, higher voltage requires lower current. So if you’re charging at 11 kw/120 V, the current required is twice as much as 11 kw/240 V. So the I^2 R losses go down by a factor of 4.
Without knowing voltages/currents on the 11 kw and 6 kw chargers, I couldn’t answer for certain. But it’s certainly possible for the 11 kw to be more efficient.