It's mostly a wash, the efficiency on the descent balances the climb, and overall you get respectably close to the same range you'd have gotten on a flat route.
I rented a mach-e recently. Went up to Snoqualamie pass from seattle. I used over 60 miles range in 10 miles on the steep part at the end, 1/6th. Going the other way I got a maybe 20% boost in distance over flat. There were a few places I was able to regen-brake, but I never had the battery go up, only stay flat. And a few times I lost enough speed that I didn't handle an interim flat well. I was extremely disappointed.
It turns out friction and drag are still things. On a pure downhill you would be able to roll, but it's not as good as going down is bad.
I also found that the car did a lot worse rolling down hill than my mini-cooper manual when I just put the clutch in, which got up to hairy speeds. Heck vehicle seemed to have more inbuilt resistance to just rolling than the fire engine I've run down that hill.
Overall I got 90 total miles of range and hit the flat at 10% battery. I was able to get 290 miles driving in seattle with the same vehicle.
That's weird. Seattle-to-Yakima at 70 mph average speed and 85 mph peak speed is about 1.5x the normal energy use for me (260 Wh/m vs 350 Wh/m). Leaving me with 20% of charge when starting at 100% (260 miles): https://imgur.com/a/Dhs38kJ
And this was during the wintertime, so with a reasonable amount of heating.
