Perfect, since my Zero draws up to 15A, not continuous. And going just by gauge can get you in trouble if you don't consider length.
Doug S said it already... but I'll restate it in my words..
from any practical standpoint, length is never an issue. sure if you have 1ft of wire and 3 feet of wire, the 3ft has 3 times the resistance.. but its also distributed over 3 times the length.. The heat generated for any given section of cord stays the same.
Now the voltage drop, sure that happens... however again for any off the shelf extension cord, of the appropriate gauge, the drop will never be enough to cause issues with the charger functioning.
So it comes down to just the gauge size. if you want to run it through a 100ft long 12ga extension cord, you can... just dont leave it coiled up, or let the fire marshal see it (because as mentioned elsewhere above, extension cords are "temporary use only".