The reason many say hook up hot feeds to add on circuits to the alt stud or anywhere between the alt and ammeter is because with the car running all of the current to the added on systems will not go thru the ammeter as it will leave the alt and go right to the added system. Coming off the battery side of the ammeter means your alt output would have to go back thru the ammeter to get to the added on systems. As was stated the only time you would have alot of current going thru the ammeter like this is if you have a dead or very low battery. You dont have to come right off the alt stud as long as you hook up the hot feed between the alt and ammeter its the same deal. Course if you bypass the ammeter and go to a voltmeter then id dont matter. Ron