Question on BMW 3-Series Alternator

Hi, I have bmw e39 2001 530i bought in march 2015 I changed the battery for her last month as it keep dropping down though the alternator read between 14.5 - 14.7 in idle should it read more than this? And till now have no idea why the old battery dies as I have no drain or faults or codes or even lights indicate in the dashboard.
my question what cause the battery to drain like this though the alternator read good and the new battery read 12.35 for 24 hours if you don't use the car.
One other thing the rear sensors beep when I put the gear stick on reverse and there are no objects behind her the front once working good any ideas?
Thank You for Your help

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This post was auto-generated based upon a question asked on our tech article page here: Pelican Technical Article: BMW Alternator Troubleshooting and Replacement

[Nick at Pelican Parts]

Your charging voltage sounds OK.
You may have a parasitic draw. You'll want to monitor the draw on the battery when the vehicle is asleep. Here is a list of the specifications: http://autotechdiagnostics.com/?p=185
Once you confirm there is a draw. You will have to isolate the circuit with the draw. Then determine which components on that circuit is causing the draw You can isolate by removing fuses. be sure to have all the latches on the doors and hood closed (pin switches) so the vehicle will sleep during testing. If it wakes up, you will have to wait until it goes to sleep again.

- Nick