Is there a legitimate use for charge mode in the Prime?

I'll ask again... What are the GPS co-ordinates of that stretch of hill where the car continues to pick up speed forever without any braking" ? Again, I remind Paul G that the car in question is a 2024 Prius Prime, not some other car. It's being driven in the normal D mode. And the phrase used by Paul G was "pick up speed" forever.

 

There are grades where you will pick up speed forever, even with all the engine braking the car can do—depending on your speed at the start.

For any downgrade, there will be a speed where your energy gain from gravity just equals what the engine can twirl off (somewhere around 13 kW in a gen 3, anyway), and engine braking can just manage to hold that speed steady. Start off below that speed, and there's plenty of engine braking to hold it or slow you. Right at that speed, holding steady is possible, and above it, you'll be picking up speed.

On a tame grade, not much to think about because whatever speed you're likely to drive will be below that critical speed.

On a very steep grade, you may have to choose a speed a lot slower than you'd like to drive, if you want the engine braking to be able to maintain it.