Cinquecento sporting Electrical problem

Hiiiillllffffeeeeeeeeeeeee!!! I really don’t know any advice and ask you for support. The following phenomenon occurs again and again: without any warning, the radio suddenly goes out, then the tap lighting weakens and finally it goes out completely. At the same time, the battery (new!) emptied itself and you can only push it to the edge. After bridging or pushing on it he ran for 3 days last time without problems, then the “fun” repeated itself. Lima works ok. 14,2V I I hope someone can help me, thank you in advance.