Its hard to say what is really going on here - if this is true battery degradation or not. As you know, when you first get the car, unless a significant number of miles have been put on the car, its considered rated miles. According to people I've spoken to at Tesla, after enough driving, it recalculates based on your actual driving habits. Whether or not this is a factual statement, I'm not entirely sure. So just say you floor it all the time, and you're using 300WH/mile. The "range" display will adjust to show you what your real mileage is and not rated mileage. But even I'm not 100% sure that is true. Its hard to tell if there is real battery degradation going on. I was told that even if you charge to 100%, which for me now takes forever (3800 miles), you're still going to get estimated real world mileage and not the rated mileage. I don't know about that. In the API for the car, there is RATED mileage listed on output. But that may not be whats displaying on the console. This is why a lot of owners forego using the mileage calculator at all and use percentages. I, however, would still like to know if the battery is degrading, and to what extent, as that would, for me, be a MAJOR ISSUE.