This study investigates the interaction between suppression, detection, ventilation, and explosion protection systems in a confined battery room to address the lack of fire safety data for building-integrated battery energy storage systems. Six large-scale fire suppression experiments were conducted in a mock-up battery room. Four suppression systems, high- and low-pressure water mist, sprinkler, and IG-541, were evaluated alongside a freeburn and gas venting scenario. Their performance was assessed based on thermal runaway propagation, temperature development, structural damage, gas accumulation, deflagration risk, and firewater contamination. IG-541 was the only system to extinguish external flames and prevent module-to-module propagation. However, explosion protection remains critical due to the accumulation of flammable gases. It is therefore essential to design inert-gas systems with a sufficient hold time and to establish a strategy for safely evacuating all flammable gases from the room once thermal runaway has fully ceased, without igniting the gas mixture. Achieving this can be challenging. The water-based systems were generally effective at cooling, but the low-pressure water mist experiment highlighted the need for optimised droplet distribution, as hot spots may lead to unit-to-unit propagation and structural damage. Ventilation prevented deflagration, but minimum airflow requirements need further study. Effective fire safety requires integrating suppression with detection, ventilation, and explosion protection, tailored to the thermal runaway characteristics