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PV is an intermittent renewable power source. Grid-connected PV inverters conventionally use grid as the energy reservoir. As the level of PV penetration increases substantially in recent years, battery is proposed as the energy storage in grid-connected PV system. This is to increase on-site consumption, which in turn avoids grid voltage rise and reduces the loss in transmission line. Additionally, it allows PV inverter to dispatch power similar to the conventional power generations. This paper analyzes the overall efficiency of grid-connected PV inverter with storage battery using system level regression models. The analysis postulates nonlinear relation between the total power loss and the battery charging. Voltage droop battery charge controller that simplifies the efficiency optimization is developed based on the regression models. The analysis and the controller are verified by the component level power loss calculations. The controller is compared in simulation to the conventional constant-current/constant-voltage battery charging using PV outdoor measurement data.