Looking at your comments, for your specific use, you'd be just fine if it's wired in directly to the junction box properly.

I'd still check and see if your charger can fit 6awg wire just so it's consistant, but at 40ft to the breaker it shouldn't be an issue.

However, that being said.... Burning your house down because of what a stranger said on reddit isn't a good idea. I'd follow up with what the other comment said on getting some involvement from professionals before moving forward with the install.