I have a 2011 A5 after an accident. Everything was replaced and fixed. The battery when tested shows that it's good. The engine starts if its boosted from another source of power but will not start on it's own although the battery is fully charged.
Anybody might know what the issue could be?

 

You may want to verify that the main grounding points are clean and tight. The added resistance from a bad ground may be your problem. Sometimes something very simple causes big problems.