I think it has to do with miles driven, battery state of charge and likely a thousand more things I don't know about. I have noticed similar behavior after a charge, and inverse behavior after sitting overnight (not plugged in). If the Roadster isn't plugged in overnight, it looses a few miles of range of course. It also looses another 10-15 miles of range in the first mile or so driven. A little bit of a range shock. I figure the range algorithm does the best it can with speed, load, available khw etc. etc. It might also have to do with the age of a battery pack. A 2008 1.5 with under 5k miles on is still a 4 year old battery pack. That might play into things a little as well?