The rapid decarbonization of the logistics sector through electrified heavy trucks presents a significant challenge for existing electrical infrastructures, particularly at charging sites constrained by low-power grid connections. This paper investigates the application of Battery Energy Storage Systems (BESS) acting as an energy buffer to decouple high-power charging demands from the upstream network, thereby mitigating grid overload and ensuring system stability. The study utilizes the technical specifications of the Vilion EnerCube (P1000C2089), a containerized solution featuring a 2089 kWh capacity and a rated output power of 1000 kW. The core of this energy strategy relies on the system's ability to act as a dynamic power multiplier. By ensuring 100% availability of its 2089 kWh energy capacity and providing a near-instantaneous response to high-power demands, the BESS effectively decouples the charging load from the grid. This allows the station to satisfy the energy-intensive duty cycles of Swedish heavy-duty vehicles, even when the primary grid connection is limited to low-power throughput. Two distinct architectural designs are evaluated. Parallel Grid-Support Integration: The BESS is integrated into the existing AC infrastructure to provide supplemental power during peak charging events, allowing for rapid deployment with minimal site modification. Series Buffer Configuration: Charging dispensers are connected directly to the BESS output. While requiring more extensive local infrastructure restructuring, this 'series separator' design minimizes redundant energy conversion stages and avoids overstressing the legacy grid components, which otherwise act as a 'bridge' for high-power transients, thereby allowing for a customized infrastructure sizing tailored to specific operational needs during the electrical design phase. The performance of these designs is simulated in Matlab/Simulink environment, using Swedish-specific operational profiles, including heavy-duty models such as the Volvo FH Electric, contrasted against high-volume Swedish passenger EVs like the Volvo XC40. Results indicate that the BESS and EMS compatibility as an eco-friendly solution for power expansion without the need for immediate, capital-intensive grid upgrades.