I do realize that regenerative breaking does not 100% cancel out the energy required to accelerate the vehicle. The Model X will be ~10% heavier and Musk has s

I do realize that regenerative breaking does not 100% cancel out the energy required to accelerate the vehicle. The Model X will be ~10% heavier and Musk has stated recently that the range is expected to be ~10% less than that of the Model S. In other words, obviously a heavier vehicle will use more power than a lighter vehicle, that's true with any fuel source, but it's a small difference in this case. They could put a battery pack with 15% more capacity in it and the range would be about the same as the Model S, but they're probably going to use the same battery as the Model S for compatibility and manufacturing reasons.