If you have a multimeter you can test it yourself (or you can get one for $40 at Home Depot). Test the battery (car off) should be above 12 volts. Then test with car on (now you are testing the alternator) should be 13.5 or more. This is not as good as an actual load tester, but it is a good way to start if you have the tool.
'07 650i Coupe - Black Sapphire Metallic
M6 bumpers, skirts & wheels
BMW M Cross Spoke Composite 101 Rims 20"
HUD, Comfort Access