The estimated range is a sliding average of your last 18-miles or so. You can think of it in the same manner as the miles-to-empty display you may have on an ICE...it is only accurate based on what you are doing now AND that you continue to do it in the future. IOW, it is a guess. How you drive the car, the temperature, the mode, where you're driving, all play into calculating the estimate, and that's all it is. People that have lots of miles on their vehicle have reported only a minor degradation of the battery pack. Also, when new, people tend to drive it more carefully (unless showing off for friends!), but as they become more familiar with the car, it's easy to use more and more of the performance available because it is there. There is a way to determine the actual capacity of the battery pack, and the dealer likely checked that, indicating that it was within normal range. Also note, I've often gotten into the car where it said 73-miles or so, driven 10, and it indicated the same or more miles to empty...it all depends on how you drive it and where...the calculation gets adjusted. As was said, though, that algorithm has been tweaked with the successive upgrades to more closely reflect reality as more and more real-time data is obtained.