I bought a 2013 Bmax (in 2016) 125 Ecoboost, Start / Stop does not work at all as I don't do sufficient milage to keep enough of a charge. Even if I charge the battery fully this feature will cease to function after the climate control has been on for 3 minutes. If I drive avoiding any heavy load such as the climate control it wil last about 2 days. Now admittedly this is a three year old battery but still seems a bit of a gimmick. I am curious if when the he EFB battery gives up a AMG would work any better. also at this time this requires Special, (costly) battery for a function that will maybe work for those doing circa 300 miles/week. I had a company BMW 320D on which at this milage/week functioned pretty much all the time. I welcome others experience with this feature.