Typical US electricity rates are around $0.10/kWh, and a baseline Model S having a 60kWh battery, so if I totally guess at a charging efficiency of 50% then a f

Typical US electricity rates are around $0.10/kWh, and a baseline Model S having a 60kWh battery, so if I totally guess at a charging efficiency of 50% then a full charge should cost somewhere in the vicinity of $12. On the 60kWh model, it costs $2000 to enable the supercharger hardware, so I can't imagine they'd lose too much money off these. Keep in mind that these aren't really intended for frequent use: they generally have been placing them on highways in between large cities, with the intent to enable the occasional long-distance road trip that would otherwise be outside the car's battery range. Even if Tesla loses a bit of money per car on average, it's probably worth it just for the value it adds to the cars in peoples' minds.