Mobile data traffic will exceed PC Internet traffic by 2020. As the number of smartphone users and the amount of data transferred per smartphone grow exponentially, limited battery power is becoming an increasingly critical problem for mobile devices which depend on the network I/O. Despite the growing body of research in power management techniques for the mobile devices at the hardware layer as well as the lower layers of the networking stack, there has been little work focusing on saving energy at the application layer for the mobile systems during network I/O. In this paper, we propose a novel technique, called FastHLA, that can achieve significant energy savings at the application layer during mobile network I/O without sacrificing the performance. FastHLA is based on historical log analysis and real-time dynamic tuning of mobile data transfers to achieve the optimization goal. FastHLA can increase the data transfer throughout by up to 10X and decrease the energy consumption by up to 5X compared to state-of-the-art HTTP/2.0 transfers.