That's not true. You seem to think it is calculated once at the start and then stays unchanged for the next 2-3 hours of driving, despite big changes in rain or wind drastically changing your energy usage as you drive. That is not at all how that works. That remaining % number is continually updated several times per minute the whole time you are driving! So if it starts raining heavily or a big headwind picks up, you will definitely see that remaining % start dropping rapidly in the next couple of minutes as the car notices the current energy use going up much higher and re-projects that out over the rest of the trip.

I am well aware that it's not calculated once at the start of the drive and is then unchanged. I am well aware that it updates the final battery level in both of those places. But that update is still not consumption based, it's only based on the Nav's estimate of the trip and the current battery state.

Example: I plot a trip with my starting battery at 80%, and it predicts that I will complete the trip with 20% of battery left. I start driving. Exactly halfway through the trip distance, by the original prediction line, I should be at 50% battery. (Let's assume that on this trip the line is linear -- it isn't always so, due to elevation changes and speed changes, but for the purposes of this discussion let's assume that it is).

OK, so the car originally predicted I should have used 30% of the battery at the halfway point, for a total of (80-30 = 50%) battery remaining. But, due to heavy consumption (for any reason -- rain, wind, etc.), I actually used 35% of the battery so I'm now actually at 45%, not 50%. The extra consumption caused me to use an extra 5% of the battery.

If you go look at the prediction line, it's updated to show that the new prediction is that I will arrive at the destination with 5% less battery than originally predicted, thus 15% remaining, not 20%.

__But that's inaccurate__. The heavier consumption is still not figured into the prediction -- only the fact that I'm starting from this point with 5% less battery. What's really going to happen is that due to heavier consumption, I'm going to use an extra 5% battery on the 2nd half of the trip just like I did on the 1st half, so I'm really going to arrive with 10% battery, not 15%.

You can prove this to yourself by doing this: At the halfway point of the trip, cancel the Nav, then start it again to the same destination. The new prediction will still be what the Nav would predict for a "nominal" drive, not taking into account the past increased consumption. In this example, at the halfway point, it originally has updated the final battery level to 15%, I cancel the trip, start it again, and the final predicted battery level is still 15%, not 10% as it would be if it considered that I'm going through heavier consumption.

The bottom line is that the Nav predictions do not take into account past consumption -- they only predict based on the elevation changes, speed changes, and route (i.e. anything that can be derived from the map).