Looks like around 10%. https://www.edmunds.com/car-reviews/features/do-stop-start-systems-really-save-fuel.html https://www.edmunds.com/car-reviews/features/do

Looks like around 10%. https://www.edmunds.com/car-reviews/features/do-stop-start-systems-really-save-fuel.html https://www.edmunds.com/car-reviews/features/do-stop-start-s...