What causes power loss when the car is not running? Both batteries replaced

What is your question?

When I open the door their is no power but when I put the key in the ignition to start it I get power and the car starts. But it eventually does the same thing. Tha car is just siting when it does this. I have already had both batteries replaced. One is used and the other one is new. I had a new stater put on also. What could be the issue with what it seems to be a battery issue or connection issue.