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This paper presents a single-phase battery energy storage system (BESS) with power decoupling feature on the battery side. The purpose of the BESS is to support the frequency in autonomous microgrids (MG) based on renewable energy sources. Moreover, many times it has to share the reactive and nonlinear loads, thus controlling the voltage shape and value. Furthermore, it has to be able to provide the short circuit current needed for a classical protection system. Two main topologies are of interest and one of them is found optimal. An active power decoupling circuit (APDC) is added to it in order to attenuate the current ripple of twice the grid frequency, which inevitable appears in single-phase systems and it circulates through the battery, which worsens its performances in time. A new control structure for the APDC is developed, including a current harmonic compensation in the case of nonlinear load sharing of the BESS. Experimental results are presented, showing that the proposed APDC ensures a smooth battery current, both for linear and nonlinear loads.