Unfortunately, very little.

I went back to look for my notes on this and this is what I experienced: The Fiat would use up about 30-40 miles of indicated range to go uphill less than 10 miles. But it would only regenerate 2-3 miles (of indicated range) on the downhill side.

Not my experience in my Zoe. You get nearly all of it back on the long climb and then descent which I often used to do before I moved.