This paper proposes an alternating battery discharge method by balancing discharge time of battery cells, which significantly increases battery lifetime. In the conventional method, several battery cells are alternately discharged to make battery recovery effect, and this increases battery lifetime. In this case, there are some overlap intervals where several battery cells are ON to avoid system power cut-off, but this makes several problems due to the voltage differences of battery cells. To mitigate these problems, discharge time of battery cells are controlled to make battery cell voltages as equal as possible. Measurements show that the battery lifetime is exxtended by 19.2% in the proposed method.