Think of it like a high school physics problem. When you’re up in the mountains, you have a lot of potential energy. You want to turn that into kinetic energy. The question is: later or now?

If you want it later, you can capture the energy in the battery (regen). But charging and discharging are not 100% efficient, so you lose some of it along the way.

Using it now by converting directly to kinetic energy (coasting) avoids that. So in theory, it’s superior. But in practice, you probably can’t gain speed forever (speed limits and traffic and safety and all that).

So I’d coast as much as possible, using regen only when necessary to adjust speed for the conditions.

You’re ALWAYS most efficient going slow (continues to increase all the way down to 30mph or so).

You’re NEVER most efficient constantly romping on the gas and then letting go.

Set your speed and go with it.

Set your speed control.

Your energy difference is not worth a speeding ticket or pissing off other drivers.

I’ve got to admit, it sounds like a strange question to me. When I went driving in the mountains, I used the one-pedal driving (the only way my Tesla is set up), and I went the speed that I wanted to go (not super fast), and the car recovered whatever energy it was going to recover, and it was all good.

When I was at the top of Pikes Peak (a very fun drive BTW), I had 16% battery charge. By the time I made it down to Colorado Springs, it was reading 28%.

I also went over Guanella Pass, another fun drive, and at the observation stop, at the highest point of the pass, I parked next to a Leaf. I was surprised to see it there, and the driver admitted that was about the end of its range, but he didn’t seem concerned at all about getting home. Well, no wonder. . . I mean, if it was all downhill, then no problem.