ECO mode ON or OFF

I was curious since I never owned a car with start/stop. But how long does it take for the car to decide to turn off? And does the car lurch or have issues if you hit the gas the moment the car goes off (like at a light that goes green too quickly or a stop sign where the oncoming car suddenly blinks so you're now free to go sooner than expected)?

And have any of your guys run through enough fillups with both modes to know the rough difference between the two (in terms of mpg)?

With regards to the battery though, it shouldn't drain it since the battery should keep enough charge to last for a while, unless obviously it is old. I'm thinking though what you meant was that with start/stop it would go through significantly more charge/discharge cycles, which in the past was notorious for killing those rechargeable AA and AAA batteries we all use? That I am a bit concerned myself since cars now usually don't have to discharge the battery continuously since the alternators now can usually supply enough electrical power to keep things like AC, stereo, lights, etc all going at once. I'm curious about this one as well.

Now that my CLA45 is broken in, I am actually getting at times up to 35 MPG (based on the computer and rough pump calculations) if I only drive during commutes (i.e. I use my other car for the weekends in the city). My commute is about 65 miles round trip, about 60% highway, 30% hilly winding roads (gain and lose about 300 meters in elevation), and 10% small town but with only a few complete stops. However if I decide to take the really winding roads and have fun over that 30% I can plummet the MPG down to 24 (If I really thrash the car I can get it to the high teens). I still average anywhere from 30-32 MPG, even when I use it on the weekends. Pretty good for a 2 liter 355 hp car that is actually pretty heavy. It's hard for me to predict when ECO mode will shut off the engine as there are times when I know the battery has a full charge and I have minimal electrics on (no defroster, AC, etc) and it'll take a minute at a light to turn off and other times it'll shut off the second I come to a complete stop. But even on commutes where the engine didn't stop once I'm still getting in the low 30s for MPG per trip computer.

And with my tires over-inflated (due to the very cold mornings and hot afternoons here), that means I'm probably getting even better MPG than calculated!