Battery charging

[EOD Guy]

I recently purchased a 03, X5 and the battery went dead, I removed the battery and put it on a slow trickle charge, replaced it and wa=la the battery went dead again (1 day), I replaced the battery with the one out of my Z3 and the battery light is still on. Alternator? now the transmission protection mode light came on and the ABS lights are going carzy. I'v'e had it for 7 days, I bought it as is, and the owner of CornerStone Auto, Chattanogga TN, said "sucks to be you". Is there something I can try or dealer only? Anyone know about TN law concerning used auto sales. I pulled the following codes but don't know what they mean: P0a50 = supply voltage, P1033 = charging code, P118d= EGS, P1190 = Supply voltage, P11bd=Electric Brakes, P11bf= internal fault, P2309=?, P2310=?, P2512=Steering short, P39cc=Idle control, P7c22=?

Help Please

[Zulu95]

If the light is on with the engine running at a fast idle (>1000 RPM) then I would suspect a faulty alternator. You can check it with a voltmeter. If the alternator is charging it should read around 13.85 Volts as described above.
Note. Bosch alternators charge at a lower rate that most other makes. The others usually show as much as 14.5 Volts when charging.
There was an article in Roundel last year that gave a DIY on boosting the Bosch charge to over 14 Volts.