A friend of mine spent $14 for 75 miles of range at a supercharger the other day, that's $0.1866 a mile. IDK if that's because there is a fixed connecting fee then a KWh cost added or what.
There is no fixed fee. There are two different methods that Superchargers use to charge for electricity and that's driven by the laws on the state in which they are installed.
Some states, like TN, prohibit reselling electricity by the kWh. In those states, the Superchargers charge by the minute. Because the rate of charge varies significantly based on the battery's state-of-charge (SoC), the rate is divided into several tiers based on charging speed and is prorated by the minute. i.e. For each minute of charging, the average charging speed is calculated for that minute and then that minute is charged at the tier for that average rate.
In states that allow, Supercharging is billed by the kWh. In areas where electrical demand is an issue, the rate may change based on the time of day. I've heard of this being used in California. In California, the daytime rate has been relatively high, with more reasonable rates at night, to drive flexible demand to the off-peak hours.
How much does it cost to Supercharge? There is no easy answer. Where electricity is expensive, Supercharging is expensive. Where it's relatively cheap, it's cheap. Just like gasoline. In almost all cases, it is cheaper than gasoline for a similarly sized car. Often it is half the cost of gasoline.
How did your friend determine that he added 75 miles for $14? If he's going by the mileage display, that's based on the EPA's consumption rate which may be higher, or lower, than what he will get depending on the speed at which he drives, the change in elevation, and the temperature. That figure is worthless, IMO, other than comparing the range of different Tesla models. (You can't even compare with non-Tesla EVs as the EPA process allows too much variation so it isn't consistent from one manufacturer to another) Paying too much (any) attention to that metric just adds to people's confusion. Use the car's Energy screen to get real data on your energy consumption and very accurate predictions on energy usage on any trip that's entered into the car's navigation.
Instead of MPG, the metric for a Tesla is Wh/mi. (Watt-hours per mile) Some other cars use mi/kWh (miles per Kilowatt-hour) but you can easily convert back and forth. My car exceeds its EPA efficiency/range rating in the 50mph to 55mph range. As you go faster, drag increases and efficiency and range are reduced. I haven't tested lower speeds. For city driving, the regenerative braking recovers a significant amount of energy when you slow and stop. That makes EVs, and hybrids that rely heavily on their EV mode in city driving, very efficient around town. (I once saw my SoC increase five percentage points from regen-braking while descending from about 5,000' to around 2,000')
Unless you're a person who is road tripping multiple times per month, the cost of Supercharging probably won't make much difference to you. Almost all of your charging is done at home paying your local utility rate. I've owned my Model 3 for just over a year and have Supercharged exactly twice. My car (Model 3 Long Range with 18" wheels) has averaged 0.264 Wh/mi (3.79 mi/kWh) since new. My electric rate is about 10¢/kWh so I'm paying about $0.0264 per mile for electricity.
People who have never lived with an EV are often confused by EVs because so many of the conventions they've learned from driving ICE cars for years don't apply. There are so many misconceptions out there.
