If I were doing 400 miles in a day, I'm not sure where outside of maybe Northern Alaska I wouldn't hit several Tesla super charger banks over the course of 100 miles. I've never seen one out of order in 2 years. Being that you'd be doing that in a day, you'd be wanting a fast charger not a level 2 or you'd be sitting hours waiting for a charge with that kind of mileage. The biggest stretch I ever go between charger banks is between Nephi and Beaver, UT and technically if I was in a pinch I could pull off to Richfield or use an adapter in Scipio. If you have a Tesla and your concern is I drive too much in a day that shouldn't be a concern. If you're in a Kia and Hyundai it might be harder until Tesla opens up but most OOO chargers I see are level 2's