Citroen DS5 Battery Problems

Screen goes blank radio doesn't work nothing shows on the screen, when I leave it overnight it comes on the next morning then when I stop it again it goes off.

I have an intermittent beep sound from somewhere inside car. Thought it maybe my battery in key but it isn’t. No warning on dashboard. Does anyone have any idea what to check? Thanks

The screen comes on ok but after a few minutes messages come up on it like ‘insert cd’ and then I lose everything.

Electrical circuit warning light on.Car all runs fine. Previously came on for 2 days and went off. Now been on for a few weeks.recent mot and service done.