Yesterday night the following happened to me. I drove about 80km at the track over autobahn. Turned off the car then and came back to the car about 2 hours later and wanted to drive away. Have keylessgo in the vehicle. So at the door handle, car locked up normally. Reinset brake kicked start button pressed, then the starter went through in normal pace twice but did not start. I then repeated the again 3-4 times with always the same result. I tried it again twice with the key directly in the ignition lock but also that showed the same symptoms (cause 2-3 times went through but no start). So someone stopped for starting aid. Since I am absolutely lay about cars and technology so stupidly connected to the rear battery start aid (which I only learned later this was wrong). Long talk short sense car jumped immediately. I had the days before when the SL two days ago, the comfort battery turned off the functions. But she disappeared after a few minutes after the car started. The rear battery was from 2016. Now my question may be that the comfort battery weakened, and because of the wrong start aid that had enough juice again? Or was that just a coincidence that the SL started and the error is to be found elsewhere? SL 500 Year of construction 2003 Edit: battery in front has 12.6 volt. battery in the rear 12.1 volt. I just measured Thank you in advance for any help