I had a MINI PHEV for 48 hrs, the battery ran out in 30 mins so for 47 1/2 hours it was running on a 1.5 underpowered petrol engine. No amount of energy recuperation will make up for plugging it in, and if you can’t plug it in or need to travel more than 20 to 30 miles it will not do 100mpg it will do 25mpg