Is this really true? I thought these batteries could take as much power as you could put into them. Hence V3 charging facilities coming about with no hardware changes required.
Batteries can
not accept arbitrarily high charge rates. As evidence, consider that the older Model S and Model X, and even the SR/SR+ and MR variants of the Model 3, can't use the full 250kW of the V3 Supercharger. Also, consider that all EVs taper down their DC fast charge rates as their batteries' SoC rises. All these things happen, at least in part, to protect the batteries; at a high SoC, it's unsafe to pump power into them too fast. That's true even at a low SoC; it's just that "too fast" is faster at a low SoC than it is at a high SoC.
There are other factors at play, too, like the capacity of the wiring between the charge port and the batteries. Something similar is in play in the cables on DC fast chargers; they must either get thicker with faster charging or they must become water-cooled (as is the case with Tesla's V3 Superchargers and at least some Electrify America chargers, IIRC). Although you
could make the in-car cabling more robust, that adds weight and cost -- factors that, as
@doghousePVD noted earlier, would also work against the proposal to add a second charge port to the car.
In the end, this cost factor may be the most important one. Consider the Chevy Bolt, which provides CCS DC fast charging, but only as a $750 option. Of course, it's entirely possible that Chevy is ripping people off with that pricing, or that some aspects of that extra cost would not be obviated for a second charge port; but if that's what a DC fast charge port really costs, do you really want to spend that much for a second charge port, in the hopes of being able to occasionally "double dip" to drop your charge time from 30 minutes to (optimistically) 15 minutes? (It'd probably be a smaller improvement than that, in practice.) Personally, I'd rather see improvements to the single DC fast charge speed -- get the Model S, X, and 3 SR/SR+ speeds up so that they can take full advantage of the V3 Supercharger; do the R&D and improvements for a V4 Supercharger; and make changes in the CCS and CHAdeMO worlds so that those vehicles can take advantage of the 350kW CCS and/or talked-about-but-not-yet-deployed 400kW CHAdeMO standards. I'm guessing that all these things are happening -- certainly manufacturers have announced soon-to-be-released cars with faster CCS and CHAdeMO charge speeds than is common today. It'll take time to do the necessary R&D and get the updated vehicles into production, as well as the DC fast charging infrastructure to support the new cars. Tesla is ahead of the curve on this, but they can only push the technology forward so fast.
