BMW Repair: 2002 325i battery dies, negative cable, positive cable

Question
I own a 2002 325i with about 57000 miles...recently ive had a problem with
the battery...one day the batter just died and the car wouldnt start...i jump
started it and it ran fine for a while but then died after a couple of hours...i
ended up buying a new bmw battery from the dealer...installed it and it
worked fine but the battery kept dying...i did this two more times with two
more batteries and the car kept dying..after i took the car to my mechanic he
couldnt find anything wrong with the car and told me that the alternator was
fine....he gave me a battery and the car has been running fine but the other
night the battery light on my dash board kept flashing...i  went into my drunk
to see if the connections werent tight but when i touched the negative cable it
was hot...my questions is...any ideas on what is draining the battery since the
alternator works??

Answer
Alex if the battery has become discharged while driving with a dash battery light on then replace the alternator. Our alternator are all to commonly intermittently faulty. If the car has never had another alternator in it during all this battery carnage the alternator replacement is way past due. Make sure the battery connections are clean and tight. Make sure the engine ground to the frame is good and tight and lastly make sure the positive cable connection way up on top of the starter motor is tight. Any one of these will cause the car not to charge.
-Evan