In my Model 3 I’ve juiced at Wytheville a few times, none of them for free. The rate is $0.21/kWh. The only supercharger that has been a no charge fill for me was Lima, OH. Other SC’s in OH did charge so I don’t know why Lima didn’t, but I liked it.
Another interesting (to me) factoid is that I charged once at the Greenville, South Carolina supercharger for free, and at another time was charged $0.20/min. Don’t know why but could have been whatever my state of charge was, though I don’t recall these numbers. All of the other dozen or so SC’s in MI, OH, WV, VA, NC, SC, GA, and FL I’ve used have charged my credit card, and charged consistently.