On good days, you can definitely make it if you keep your speed down. But part of the problem is, like AWDTesla hints, that you can't predict the bad days - because a day that looks like a good day might have, say, surprise headwinds. If it was a nice day and I was doing it once I might try the 200 mile trip. But I wouldn't do it on a regular basis (at least not in a 70) without a known place to stop along the way. Not all leave as much buffer as I do; but I want to make sure I never run out and in fact I don't even want to worry about whether or not I will make it while I am driving. If you do fall short, it usually won't be by much; so if there is a charger you can count on that is, say, 75-80% of the way you could use that only in emergencies, and you shouldn't have to be there too long.