Tesla Motors Club

I know that charging speed is faster at lower soc than at higher soc, but is there a difference in the amount of energy required to charge each % of battery at different soc -- that is, does it require about the same amount of kwh to charge each additional 1kwh or 1% at 10% capacity compared to at 90%? And is it close to 1:1 inpututput, or is it significantly less efficient than that?