A control method for prolonging the service life of battery bank in stand-alone renewable energy system using Electric Double Layer Capacitor (EDLC) is presented. Recently, it has become one of the main problem needed to be solved urgently in future stand-alone renewable energy system that the service life of battery bank is shortened due to the fluctuant output power caused by varied weather condition, with higher cost and power loss. In this paper, to prolong the service life of battery bank by realizing smoothed power supply to battery bank, a bi-directional Buck/Boost topology and its control method using Electric Double Layer Capacitor (EDLC) is proposed, Simulation in PSIM and experiment are carried out in order to confirm the validity of the proposed method. And the simulation parameters range is identified according to the smooth level of battery current output. The experiment result is better agreed with the anticipated design and simulation results when the higher harmonic frequency varies under the appointed range of frequency and fluctuation amplitude [1].