For many years there has been a trend to increased electrical energy management in cars caused by the replacement of mechanical parts by electronic or mechanical devices as well as the introduction of new electronic features. Whereas the number of electrical consumers contains to increase, the battery is still the only passive power source available. Because of this reason, needs for driving power of the engine accessories such as alternator system have increase bring about additional fuel economy. To imorove these system global car makers develops new controlled alternator system. This paper focuses on battery life times improvement and fuel economy improvement according to control of alternator. In this paper, Development engineers are performed on effect of type of alternator system on battery life time and fuel economy by experiment. And it is also calculated the effect on vehicle charge and discharge status and fuel economy using exhaust cell and hot wind tunnel with FTP Mode and EEM specification. As a result, 1.7% of vehicle fuel economy improvement and battery life time’s 8% improvernent can be achieved in a vehicle with controlled alternator.