Multiple uses of the Supercharger does not harm the Model S battery because the Supercharger computer and the Model S battery computer work together to protect the battery during charging. Also, since most Supercharger stations are solar powered, Tesla pays nothing for electricity and can provide free electricity "forever", as they have promised.
The reasoning behind the Supercharger network is that most people driving long distance can drive about 3 to 4 hours before needing to stop for a break of 20+ minutes. A Tesla owner can easily start their journey in the morning at 8am, drive non-stop until lunch and charge their car while they have lunch. Then, after lunch, they can keep driving until dinner, charge their car during dinner, and keep going if they want.
Potentially driving range in a day is at least 1200+ km (400+ km x 3), with no hassles or wasted time charging the car.
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