What charge rate are you charging at? 12A, 16A? At any rate, I've used a 25' 12 gauge for 16A charging. Works fine.
One caveat. After about a year of charging off a 120V 20A outdoor GFCI receptacle at 16A (one with the horizontal slot), it caught fire and burned up. Fire was contained in the metal receptacle enclosure, but you could see smoke damage outside it. I replaced it all with a new heavy duty 20A receptacle (no GFCI), and have been charging one of our Teslas at 16A since, with no apparent problem (note that EVSEs, like Tesla's Mobile Connector, have a built in GFCI). I don't know if the GFCI just died, or the wire connection to the GFCI worked its way loose.