Battery Energy Storage Systems (BESS), based on lithium-ion technology, offer a sustainable and cost-effective alternative to diesel generators in data centers. BESS enables fast switchover during outages, reduces space and construction costs, and supports grid stability. It also opens revenue opportunities via frequency regulation markets. Though runtime is limited, combining BESS with cloud infrastructure ensures operational autonomy. As battery costs fall and adoption grows, BESS helps future-proof data centers, reduce emissions, and support a fully decarbonized digital ecosystem.