[Sean Marconette]

The battery capacity has a lot to do with the load induced on the alternator. Think of it as the battery being a bucket, the bigger the bucket the more capacity it has, and does not ask the alternator for any more amperage than is being used to maintain the battery charge. The voltage from the alternator is also higher than the load from the battery. The higher the voltage the smaller the wire needed. Look at the overhead power lines coming from your local power plant they are extremely small diameter due to the voltage they are carrying.

Sean