The increasing demand for efficient and intelligent battery charging solutions in grid-connected systems presents challenges in maintaining power quality, voltage stability, and battery safety. Traditional chargers often lack the adaptability needed to respond to fluctuating grid conditions and varying battery states, resulting in reduced performance and potential battery degradation. This paper presents a dual-stage gridconnected battery charging system that combines a buck-boost DC-DC converter with a three-phase inverter. The system is governed by a unified control strategy utilizing Clark-Park transformation and PI-based controllers. The buck-boost converter regulates the DC-link voltage, enabling both buck and boost operation to accommodate a wide range of battery voltages. The inverter interfaces with the AC grid using synchronous reference frame (dq-axis) control to ensure compliant and stable power delivery. A control logic module manages smooth transitions between Constant Current (CC) and Constant Voltage (CV) charging modes based on real-time State of Charge (SOC) data. Simulation results confirm that the proposed system achieves reliable, safe, and efficient charging across diverse grid and battery conditions with 93.5% efficiency and THD less than 3.5%. This architecture is well-suited for electric vehicle charging stations, grid-tied energy storage systems, and smart power infrastructure requiring adaptive battery charging control.