Even using Pure EV mode, on the Volvo, if you accelerate beyond the electric motors ability to make progress, the car will switch to normal hybrid mode and the engine will start. You are not left without power. One of my routes out of Bournemouth is on an upward incline with a 50 limit for a couple of miles. Until I get to the end of the 50 limit, the car will choose to stay on battery, once I accelerate up to 70 the engine kicks in. In normal hybrid mode the engine will cut in and out when needed. It’s surprising how much it’s not needed. On a long journey the car is putting energy back in the battery and using it up again, so like a normal hybrid, and the engine will stop if there’s battery to use and demands are low. I think that goes a long way to compensating for the extra weight and why our MPG figures are good.
The 3 cylinder engine on the Volvo is noticeable in low speed driving (with a depleted battery) but otherwise not particularly otherwise unless you go full throttle when it’s not unpleasant just different.
On any journey, the journal in the Volvo app shows how much battery you’ve used, how much has gone back into the battery and how much petrol you’ve used. Every trip’s different of course so it’s hard to quantify.