The increasing amount of renewable energy in power systems poses challenges for the system operators to handle the volatility of power generation. Demand response and lithium-ion (Li-ion) based battery systems have been suggested as a promising solution to provide balancing services to address this challenge. In the paper we investigate the economic feasibility of providing primary regulation services with dual-purposed Li-ion batteries in the power protection systems of data centers. This is also compared with investments in dedicated battery energy storages. Our analysis shows that investments in dual-purpose data center batteries have a higher profitability, even if this means that the battery capacities in the power protection systems have to be oversized with respect to the data center backup time requirements.