In this paper, the authors present an energy efficient design and an operational method for a Li-ion battery powered wireless telecommunication power system. Wireless telecommunication service providers have strived for reducing the OPerating EXpenditure (OPEX) of their Base Transceiver Stations (BTSs) because an urban BTS consumes more power as the data uses of mobile subscribers increase in these days. Thus, in order to reduce the OPEX, mobile service providers have studied for a green BTS which uses less electricity from the main power grid for its normal operation with renewable or alternative energy sources.