Neil Mitchener

Hello there. I'm Neil Mitchener, and recently aquired my BMW 530i SE fvrom my Sister and Brother in law. The battery goes flat after a few days, yet is fully charged, say beginning of a week, and although not using my car for a week, it goes quite down, sometimes flat. Often the CD player wont work too if battery not 100%. Please advise anyone please. Rgds Neil in Poole