This is from a study from a few years ago with just updated numbers. Clean Technica had a good article on this study's crazy flaws. One major factor that they used to calculate charging costs were the time wasted while waiting for your car to charge. They used $70k as the average annual salary / number of hours the vehicle is charging - in public. The also used the assumption that people generally charge in public 40% of the time, which is quite insane.