85% charging efficiency.... ok I see you mention other people throw out that number and it might be correct. My personal experience has been better. At my electrical panel, I can monitor energy delivered to my car and compared that to what I actually got. I regularly see about a 7% loss on my X100 during the charge event. I charge at about 40 amps on my HPWC and realize that when charging at a higher current, there is greater loss. I suppose you can use the 15% number and may be correct and I doubt the tax man is going to dispute you ;-)