2008 BMW 535xi BATTERY DRAINING FAST NOT CHARGING

[ruvinsonfr@gmail.com]

My 08 BMW 535xi is not holding voltage in the battery. Im pretty sure it has a short to ground somewhere but I can't seem to find it. When I jumped the car since the battery is dead it would start up but as soon as you take the jumpers off the battery will drain in a couple seconds. If I charge the battery first and then start the car, it will start and then slowly drain the battery, so the alternator is not charging. I tried replacing the alternator with a brand new OEM Bosch one and still nothing. I noticed my ground cable on the passenger side was corroded out so I got a brand new OEM cable from bmw and replaced it. Still nothing. I have no idea where the short is coming from. any ideas how to find it?