how old is your BM
a freind of mine recently had a charging issue with his bmw 525d e60
he went to kwik fit who told him that his alternator had packed up and due to that the battery also had died
anyways they replaced the alternaator and battery and off he went
2 days later and the same problem
so he went back to kwik fit who said the alternator had packed up and maybe it was a dodgy one so they repced it free of charge
as he drove out 2 mlies down the road and battery light on again
kwik fit then recomended that he leave the car and further diagnoses would be done
after inspection by there so called specialst, kwik fit said some charging sender unit relay type thing had failed and needed changing so another £190.
and after that guess what, yep same thing,
by this time he had enough and though might uswell go to bmw,
now, bmw told him that these cars are installed with some smart charging circuitry and the car needs to be told when a new battery is fitted,
obviously kwik fit didnt know this
however bmw done thier thing wacked him with a bill of £300+ for some relays that had gone due to kwik fit erroe and all is now well.
his case with kwik fit continues