2013 Q5. Drove home and parked no problem. In morning car completely dead. Attempted to put battery on charger. But indicated battery already charged. Jump started car no problem. Will only start with jump.

I would assume dead battery, but no idea what would have drained it. Also, car is not trying to turnover or showing dimmed lights or any typical indicators of dead battery. When I open door, no lights, no sounds. completely dead

TIA

 

Make sure the battery terminals and cables are clean. Also, has the battery been loaded tested?