I would like to know the same thing, we recently had an incident (again) where we woke up in the morning and the starter battery was dead, this is the second time this has happened and the first time we know the reason, namely that we left the key in position one when we went to bed. But the second time, recently in France, the same thing happened, the leisure battery worked, we had the cooling on, lights and heating were ok, but the roof could not be closed and the car could not be started. Just calling the Mercedes technician and after five hours we got the car running again. Now I'm starting to wonder, can't you replace the starter battery with the leisure battery in a situation like this? Since it seems to be the same type, it should work right?