I think I see your confusion, MN... the method of wiring makes you think that the current flows
through the battery. This is simply not the case.
As long as the current doesn't blow a fuse or fusible link, they can be discounted. So then, a simple diagram would have the alternator, battery, and the rest of the car (the load) all in parallel circuit. The potential available on the positive lead is the same potential available for everything... both the battery and the car and its accessories. If the electrons are needed by the headlights, they most
certainly do not flow first from the alternator, into the battery, then out to the headlights. The vast majority travel directly from the alternator to the headlights, with a tiny percentage being supplied by the battery to fill in the ripple.
One last thought... many cars have the battery remotely located from the engine compartment, such as a boxster. The load presented to the alternator by the engine and accessories is closer, via wiring, to the alternator than to the battery. The power doesn't first flow down the longer cable, "through" the battery, then back to the rest of the car. Electrically, it just doesn't happen the way you describe. Those electrons just aren't that smart.
Jack
BTW... I guess I should explain... I'm an EE. Electricity is my "thing".
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