The increasing demand to reduce pollutant emissions and the drive towards decarbonization are convincing utilities to integrate more Battery Energy Storage Systems (BESSs) with grid-forming capabilities. An interesting example of this trend is placed in Porto Santo Island, where Empresa de Electricidade da Madeira (EEM), the grid operator, has installed two grid-forming BESS plants in recent years, the first one is a 5.4 MVA plant, while the second one is 12 MVA and these are interesting numbers if compared to the load peak power which is around 8 MW. This study aims to demonstrate how these plants can ensure stable grid operations when a well-tuned Virtual Generator Mode (VGM) control is implemented, and to outline the process for achieving optimal control tuning to meet utility requirements. A tuning approach with incremental complexity is used: firstly, an aggregate-analytical model is developed to describe the main dynamics of the system; then dedicated simulation studies of the plant are developed in PSCAD and PowerFactory to study control instabilities given by multiple-converters interaction; finally, an ultimate validation is performed with real time HIL test bench. The parameters derived from these studies are applied to the actual plant, and the results are compared to the analytical predictions, showing proper alignment. This case study on Porto Santo Island provides significant knowledge of the practical application of grid-forming BESS plants. It highlights how a proper designed and tuned BESS can maintain grid stability without other traditional synchronous machines connected to the grid. The findings underline the potential of BESS to play a crucial role in the transition to a more sustainable and resilient energy grid. The successful implementation of grid-forming BESS on Porto Santo Island, enabled by Hitachi Energy PCS and automation platforms, serves as a model for other utilities aiming to enhance grid stability while reducing reliance on fossil fuels. By adopting similar approaches, utilities can achieve significant environmental benefits and operational efficiencies. This study not only contributes to the body of knowledge on BESS integration but also provides a practical framework for future projects aiming to push advanced energy storage technologies for grid stability and sustainability. In conclusion, the Porto Santo Island project shows the effectiveness of grid-forming BESS in ensuring stable and reliable grid operations as load sharing or frequency regulation. The alignment between measurements from the field and analytical-simulative studies confirms the robustness of the proposed modelling and tuning approach. This work demonstrates that with proper knowhow, BESS can be a key enabler of modern, decarbonized energy systems, laying the foundations for a cleaner and more sustainable future.