For anyone looking for a location that will refill CO2 tanks instead of only swapping, Simplex Grinnell is excellent. They are located off the Arrowood Rd Exit on I-77 in an office park.
Their address for mapping purposes is:
9826 Southern Pine Boulevard, Charlotte, NC
Go to the very back of the office complex and Simplex Grinnell will be on the right. For refills, drive around to the back left side of the building where the loading docks are located. They will refill while you wait, and they were very friendly. They only take debit or credit cards if you don't have an account with them.
As it turned out, they're office park is directly across from my office park. Also, Burkert (maker of solenoids used in many of our regulators) has an office in Charlotte a few blocks away in the Whitehall business park. I'm surrounded.
If you go to Simplex Grinnell, check out the wild eleocharis growing in the median in front of the traffic light for the entrance to the office complex. That median stays submerged most of the time, and you can see the eleocharis as it is darker in color than the surrounding grass. It's quite a stand.
I hope this helps those getting into pressurized CO2 in the Charlotte area, and best of luck on your tanks.