In the evolving energy landscape marked by a surge in electric vehicle (EV) adoption, efficient and rapid charging infrastructure becomes imperative. Ultra-Fast Charging Stations (UFCS) employing Direct Current (DC) have arisen as a pivotal solution to this challenge, primarily due to their ability to deliver high power and reduce charging times substantially compared to traditional Alternating Current (AC) charging methods. Moreover, the DC bus system allows for greater compatibility with renewable energy sources and storage systems, presenting a seamless interface that bypasses the need for recurrent AC-DC conversions, thus enhancing efficiency and flexibility.

Against this backdrop, this research investigates the techno-economic feasibility of integrating Battery Energy Storage Systems (BESS) with a DC UFCS, factoring in current technological constraints and prevailing market conditions. The study was inspired by the pressing need to alleviate grid congestion, notably in areas like the Netherlands, and the prospective role of BESS in achieving significant cost and energy savings. An analytical energy model was employed alongside a physical battery model to rigorously evaluate the performance outcomes of the proposed integration. Leveraging a dual simplex algorithm, the research capitalizes on the price oscillations in the day-ahead market, optimizing the BESS's charging during low-price windows and discharging when prices escalate, enabling a substantial energy cost reduction, with savings up to 49\% in certain scenarios.

Next to energy cost reduction a grid searching optimization is employed to work in a peak shaving function to alleviate peak demand on the grid while subsequently reducing network operator costs by up to 79\%.

This reduction in operational costs will be compared against the large capital investment cost associated with such \gls{BESS} to examine whether the reduction in operational costs is more significant than the upfront costs they come with

Additionally, the research examines the intricacies of battery aging vis-à-vis its operational patterns. The findings reveal that batteries engaged extensively in cost-saving operations tend to have a reduced lifespan due to increased cycling and higher average currents. However, larger battery configurations, which maintain lower average currents relative to their peak capacities, demonstrated more extended life cycles, thereby suggesting long-term economic viability. It was found that the lifetime of all examined configurations was significantly larger then the payback time of the systems.

In summary, when optimally sized and orchestrated, BESS can offer significant lifetime cost advantages for UFCS, with potential savings reaching upwards of 56\% for new DC UFCS installations and 46\% for existing systems. The meager performance variance (0.6\%) between the analytical model and the actual battery model further accentuates the practical viability of BESS-integrated UFCS. This research highlights the profound economic and technical benefits of merging battery systems with UFCS, advocating for their adoption as a forward-looking solution in the realm of electric mobility.