This paper presents a dynamic data-driven state of charge (SoC) management strategy for a battery energy storage system (BESS) providing fast frequency response (FFR) services. The SoC limits are continuously updated based on an expected frequency profile which is derived from a statistical analysis of real frequency data for three different power systems, namely the Continental European (CE), Great Britain (GB) and Dominican Republic (DR) power systems, spanning the period 2014-2017. Simulations presented indicate that the control scheme developed can successfully maintain the SoC of the BESS inside the desired limits while crucially providing FFR services to the grid.@en