I think regen affects hypermiling technique. For instance, imagine you're at the top of a big hill, straight road. You have been driving at 50MPH on flat roads. If you coast down in neutral, you'll hit 75MH pretty quickly and stay there for miles. You have two choices: 1) Standard Hypermiling Technique: Coast down in neutral at 75MPH. When you reach the bottom of the hill and hit flat road, you continue to coast until you hit 50MPH, then put cruise control on. 2) My Proposal: Use cruise control down the hill at 50MPH, which means regen will be engaged. When you reach the bottom of the hit and hit flat road, continue at 50MPH. In scenario #1, your "excess" potential energy goes into more speed. At the bottom of that hill, that extra speed will let you coast a little bit longer on flat land until you reach 50MPH. In scenario #2, your "excess" potential energy goes into the battery. Some of it is lost since regen isn't close to perfect, what you do capture will be greater than momentum you have at the bottom of the hill. Therefore, it's the more energy frugal way to drive. The longer the hill, the more regen will help. Now, I think it's possible on a short and/or not steep hill where the additional speed gain above 50MPH is modest and you reach max speed the foot before the road levels out, that since you haven't gained much speed there isn't much additional aero losses and so the extra momentum you have at the bottom will carry you further than the juice you got into the battery. But, I don't know where the transition point is.