I placed a alternator even hook up multireader showing all amps not charging

alternator is bad.when an alternator quits charging,then you start running off of the BATTERY,but if the alternator does not maintain the charge on the BATTERY,then the more things you turn on,a/c,headlights,heat,wipers,radio,etc,it drains the BATTERY down to NOTHING, VERY QUICK.then the vehicle cuts off,and won't start back up.a good fully charged battery with the vehicle off will have 12.6 volts on it.when it's running,the battery should have 13.5-15.0 volts on it.