I hear you, but did you ever worry about how far 1/4 or 1/8 of a tank of gas was going to get you? I just found myself fretting too much about how many miles I was getting at 90% or 100%. ...
Well the sad fact is that on 1/4 tank of gas my car can go as far as my model X can go on a full charge in the winter. The gas gauge isn't really linear, so when it reads 1/4 you often have way more than 1/4 left -- surely you've noticed that on your gas vehicles the tank stays close to "full" for quite a while, drops through the middle range almost instantly, and then seems to stick around 1/4 - 1/8th full forever? In any event my Accord can go 250+kms easily on 1/4 full. Heck it goes 75kms when the gas warning light is on! I've never had the nerve to drive our Model X below 2km (0.5%).
Going in to my 5th winter...
2. Pop open the Energy app and leave it at "Last 30 Miles / Last 50 km" and watch the Projected Range number. It will also count down as you use up the battery. (Side note: I wish the mini view of Energy on the center dash would show projected range, but it only shows the graph and average consumption number, so you have to use the app on the 17" screen).
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I like there to be a 25% minimum buffer between Actual and Projected when I set out.
I'll put a vote in for the 'fake kms' way of calculating. We've been driving our model X 300kms regularly on a route with only a single supercharger stop roughly at the midpoint. In the roughly 1.5 years we've owned it, and the 'battery in km' seems easier for my wife to grok and works well enough for me. First off the easy rule of thumb for model X is put up the trip computer and watch your average wh/km for your entire trip (not limited to the last 50kms, if you don't want to be); subtract 200, divide by 2, and that's the %age extra mileage you need. E.g. you're driving 300km, and have gone 100 so far, average wh/km showing 260, you need 30% extra range. Since you have 200km to go, that means you need the battery to show you 260.
The math behind this is simple enough. The X is rated at 210 wh/km, but you're using 260 wh/km; so really you're using an extra 50 wh/km more than rated. That's 23.8% more. But by subtracting 200 instead of 210, you give yourself a bit of buffer (not to mention making the calculation simpler). So for the model X, battery showing KMs plus this simple rule of thumb makes it pretty quick to figure out if you need to charge ... a decision you'll be making as you approach the supercharger and while you're sitting there wondering if the notification that "you have enough energy to continue on your trip" is accurate.
For me the most stressful drive ever was going from Syracuse to Buffalo back when there was no charging between them - 200kms between these SCs and I panicked and stopped at a destination charger a mere 6 miles away from the destination with my battery showing less than 4km of range left. Cost me an extra hour on an already painful drive from New York to Muskoka with a trailer in tow...
