The department of energy sponsored a study by CA Polytech about where battery Energy density was at the time, and asked for updates each year.
An interesting milestone was reached in 2009 where current EV's had a "higher deliverable mechanical energy density " due to overall powertrain weight reduction and energy efficiency.
That was for mileage under 119 miles for standard US Compact car standards. Since then that number has crept up to ~240 miles, and is expected to by 300+ miles by 2022.