I don't quite get this. It was a round-trip thing right, like the overall net elevation change at the end of the day was 0, right? All that energy was stored as potential energy, they'd get it back rolling down the mountain. To my understanding a round-trip it shouldn't have made that much of an impact.

Regen braking is not 100% efficient, closer to 70-80%. So climbing a mountain and then going down the other side does cost more net energy than driving the same distance on flat ground.

Also if the elevation change is such that you don’t have enough to get to the top, the amount you would regen on the way down doesn’t matter.

This isn't a question of regen braking through.

> climbing a mountain and then going down the other side does cost more net energy than driving the same distance on flat ground.

You say this, but your reasoning is regen braking? What if you never had to brake the entire way? Where did all the energy going going up the hill go? If I carry a sack of sand up a hill and drop it, the amount of energy it has falling is equal to the amount of energy lifting it up the hill. Why does this then magically change when that sack of sand is now a car?

Without any resistance or breaking you are correct, but in real life you do have to break. Non constant speed also makes it worse because resistance is not linear.

Resistance is the same as on flat ground. It shouldn't be making an impact in the whole going up and down the mountain. The amount of resistance you get going 10mi at 60mph is the same going up as going down as going flat. So we're still at you spent some extra energy going up, and now you have that extra energy going down.

I do get if you're needing to ride the brakes a lot you'll get a pretty big impact on range, but a lot of grades wouldn't require that.

>Resistance is the same as on flat ground

At the same speed, but if you don't break you likely won't have a constant speed. There's also motor efficiency, but that has less of an impact on electric vehicles because they are efficient over a high range.

2000ft of elevation change in 35 miles is likely to require braking.

2000ft over 35mi is like a 1% grade. That's not much of a grade.

A car will tend to gain speed on a steep descent. It is undesirable and illegal to drive down the mountain at 200mph, so you must reduce your speed.

Mechanical brakes do this by converting that energy to heat and brake dust.

Regen brakes do that by converting around 70% of that energy into battery storage to be used later.

Your sack likely does not roll down the hill with zero losses to friction along the way. The sack has the same energy as it did before you moved it, but it does not mean the journey consumed net zero energy.