With gas spiking & even SHORTAGES likely soon, I might Plug-In. :)

you can also set for 8a iirc. i would feel the connections to see if they are getting uncomfortably warm

 

IMHO: 12 gauge or lower AWG & make sure it's the only thing plugged into that circuit. It will draw 12A, so anything larger than a cell phone charger on the same circuit will trip your circuit breakers. The extension cord will heat up on the ends/connectors. If you get a bad extension cord, where they run out of copper wire mid-cord; it'll heat up there too. Use your hand or a temperature gun to check/test - an hour or two into charging. Plugging into a GFCI would also be helpful; but that power brick on your charge cord should trip; if it's doing it's job.
If you push your charge rate down to 8A; it's going to take more than 5 hrs to fully charge. Around 2 - 2.5 hours at a free mall or city building charge-point.

 

If you use an extension cord you move the feature of the EVSE brick which, without an extension cord present, monitors the power outlet temperature and shuts off charging if that connection gets too hot. The EVSE connected to an extension cord will now be monitoring the temperature of the female end of the extension cord.

It takes over 7.5 hours to charge a fully depleted battery at the 8 amp rate.

 

When I looked into cords, I settled on Voltec - US made, higher quality than all the other ones in a similar price range (like Southwire). You might find them also sold under US Wire and Cable brand.
12/3 for up to 50', 10/3 if you need longer
they have the "extreme" model for below freezing temps, but the standard one should be fine

USW 74050 12/3 50 ft. SJTW Yellow Outdoor Lighted Extension Cord | Tools4Flooring.com
U.S. Wire 99050 50 Ft. Three Conductor Artic/Tropic Cord, 12/3 Ga. SJEOW-A, 15A, Blue w/Red Stripe | B251132 - GLOBALindustrial.com