lukestern:

@SciFrog, to answer some of your concerns.

Even if you have 98kWh energy, it can differ over time and depend on condition, temperatures, etc how much of these 98kWh you actually have at your disposal. Also it affect how well the calibration of the BMS is. The consumption you see should include AC, electronics etc, but important to note is that this is all when you drive the car and it's not parked (P). So even if you take a quick stop over, idle in the car and listen to some music, this drain will be "lost" in the figures you see that show consumption. Loosing 1.4kWh as you report could be within the error margin afaik. Which temperatures do you have around where you drive right now?

To eliminate any sort of range anxiety I would start to use the Energy graph available in the car and learn how range is affected under different circumstances, driving conditions, etc and you will gain confidence quite quickly. You can set it to 10km, 25km or 50km (whatever that is in miles) and it will display how much range you have left based on your last 10,25 or 50 driven kilometers. This will be your best prediction about remaining range under the circumstances and speed that you currently drive. And if you run low on charge, slowing down will always decrease consumption a lot and get you to your destination. This is however a situation that you will never run into if you learn the limits of your particular car. The tools are very reliable and accurate, you just need to gain the confidence to trust them.

And regarding charging only to 90% I'm not sure why you do that if you have a longer trip planned? There are no issues charging to 100% or take the car down to 0% as long as you don't let the car sit on this State Of Charge levels for a long period of time. You should for instance not charge the car to 100% and then let it sit for 2 days. But if you charge it to 100% and drive off within some hours after there is absolutely no issues. It is actually even good for the battery to fully charge and discharge it now and then. Also for the accuracy of the BMS it is good to do this because if you let's say always charge between 20-80% it can result in that the BMS doesn't calculate accurate all the time.

All in all this seems like some cumbersome details, but in the real world this is most often something you even need to think about. The daily commutes are covered within the range of the battery anyway and I assume that you have Superchargers en route if you drive longer stretches? Why not just pop in for a 10 minute charge to be on the safe side?

Thank you for the response. 7% seems high for a margin of error. Temp are in the 60s... There was no idling today, just straight drive.

I use the graphs extensively to gain confidence in the estimations, which are pretty good.

These trips are daily commutes, not exceptional trips, I should really set the limit at 90% and not 100%. Anyway there are 3 super chargers on the way, but I am just trying to be on the safe side if the garage forgets to charge the car and I don’t realize it (well I can always use the other car in the garage). That’s why it would be nice to be able to do two round trips with confidence, but clearly this is not a deal breaker. But the 208 EPA range of the Etron, IF it translates in real life as the same ratio vs the 295 X EPA range, would be a deal breaker because of the winter.

Like you said, maybe it is a calibration issue. Are there tools to analyze this?