We've several times successfully used the Volta chargers at the Scottsdale Quarter garages (Scottsdale & Greenway/Hayden - where the Apple Store is; also is opposite the Kierland mall site). No issues to report other than that at least for a while a year or so ago they were consistently being used as non-charging parking spots.
Thanks for alerting that there is a Volta site at Shea & Tatum. Go there for Penzey's, Trader Joe's and sometime WholePaycheck.