The alternator of your BMW may exhibit a few nuances during vehicle operation that affect the entire electrical system. Though these problems are common, you may want to replace the alternator if you continually have battery issues in your BMW.
The alternator on your BMW may cause voltage drops across the electrical system when you use multiple electrical devices. For example, when you use both of the front seat heaters, the brightness of the headlights may fluctuate.
The bolt that mounts the BMW's alternator to the engine may cause the drive belt to break due to contact. The bolt sticks out far enough to periodically touch the drive belt during engine operation. The belt will wear down over time because of the friction.
Your BMW's alternator may not provide enough charge to your battery if you make frequent short trips in the vehicle. The alternator supplies a slight charge that only works if you drive the car for longer than a few minutes.