In the over 27,000 miles I put on my car - I have yet to get all of the charge bars in green... Maybe someday I'll see it if someone ever come out with a plug-in conversion kit for this car.
When towing at highway speed, at least for me, I have more power draw going up hill then reclaimed going downhill to maintain a safe speed, plus with the power draw from AC, air drag from the trailer, etc. So I haven't gotten to that point.
Also with the braking downhill (or anytime for that matter) - if you lightly hold pressure on the brake petal - you get (perceived) about 2-3x the drag over just coasting without the brake lights coming on and you will notice the energy meter drop to the bottom of the white bar without entering the blue bar. This is usually enough to make up for the additional momentum going downhill from the towing weight.