Of the potential energy that is required to lift the weight you will get ca 90% back. Of course you won't get the energy back that you used to travel the associated distance. In other words, if you use 10kWh "extra" to lift the car X number of feet, you'll get about 9kWh back when you drop the car the same number of feet.
Not even close if you are talking about regen braking to get used energy from the battery during the uphill back on the downhill. I’ve got 8 years in teslas in Alaska. From my house to “town” I descend ~800’ over about 4 miles and my drive to work is 7 miles top speed 45 mph. In my current model 3 LR most days I average ~325 Wh/mi round trip, use 1-2% driving to work and 4-5% going home. On flat ground same driving type I’m more like 225-240 Wh/mi.
under full regen you at best get 50% back. That is under full force regen. Going down Hatcher pass 2800’ in 15 miles I can gain 1-2% but lose 10-15% going up.
Now from what I find effects range.
Like others have said speed is #1. ICEs tend to be more efficient on the highway. EVs are more efficient around town. In the teslas I can get rated range or better running 55-60 mph. 65-70 10-15% range reduction, 70-75 more like 20-25% reduction.
up hill, like mentioned uphill is a huge hit.
cold weather. I don’t notice any real reduction in cold aside from running the heat. Sunny day clear roads 20F heat off I easily get rated range.
running the heat, It depends. First off EVs never feel warm and cozy inside when compared to an ICE. Keeping the heat set at 60-62F, I don’t notice much of a difference until if gets <0F. <0F like 25%, when it gets down to -20-30F more like 40-50%. But at those temps there are multiple factors contributing. Now if you crank the heat to 70+ Even with temps in the 20’s it can cut range by 25-40%.
headwinds make a large difference. 30-40mph headwind can cut range by 30-40%
snow covered roads. Lose fresh snow can cut range by 50%.
rain, rain that is enough to wet the roads can cut range by 20%. Heavy rain more like 40-50%.
Snowing, loose fresh snow, temps <0F, I’ve had days where I average 900-1000+ Wh/mi. That is like a 75%range reduction.
that said I’ve had teslas in Alaska for 8 years and prior to last November my closest supercharger was >2000 miles from my house. Never run out of battery.