C4 grand picasso acts like battery disconnected after 4 minutes

Why does my 2008 citroen c4 grand picasso act like the battery has been disconnected when it's not been used for a few minutes to the point the central locking doesn't work and I have to reset the date and time everytime I get in the car

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When time and date reset, this usually points to main power problems; battery, battery cables, their connections to main/auxiliary fuse panels, two main grounds - chassis and engine block. The battery must be in good condition, free of corrosion on both terminals (clean with a solution of warm water and baking soda, water rinse), examine battery positive cabling to engine fuse and starter, battery grounds from battery to chassis and chassis to engine block.

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