I recently decided I would add a Mercedes to my list of cars owned. I went out and opted for a real beast SL55 Amg. I got the car home and the next day decided to take it for a real road test and to my surprise the car would not start. I had the RAC come out to check the issue but did not manage to get it started and told me there was a voltage issue. I had the car taken to an independent, they carried out a few checks with different diagnosis over two day and finally found the SBC unit making a ticking noise and decided to unplug it and the car started. My questions are would a faulty SBC unit cause the car to not start and Drain the battery? Can the SBC unit be repaired or is replacement the only choice?