Battery is draining somehow

Start by disconnecting the battery at night first, then check the battery in the morning. Sounds as though you have an open circuit. Usually it's a light or bad connection. Sometimes the cable that runs from the battery to the starter.

Put your car in the garage at night and turn off all lights. Look all around the vehicle for signs of a light on. Usual culprits are : hood light, trunk light, interior light, etc. Something is causing a 'parasitic draw' keeping power flowing to something. Don't need engine diagnostic.....need to find the open circuit.