The paper describes the formulation and application of an Optimal Power Flow (OPF)-driven Under Frequency Load Shedding (UFLS) scheme in low-inertia power grids hosting large-scale battery energy storage systems. Thanks to the accurate prediction of the system dynamics subsequent to a large contingency, the adopted OPF-UFLS is capable of minimizing the amount of load to be shed while ensuring a safe trajectory of the system frequency and preventing nodal voltages and branch currents to violate their feasible limits. The performance of the method is assessed by using numerical simulations of a fully-modeled IEEE 39-bus low-inertia power grid with two configurations. Furthermore, the obtained results are compared with those of the UFLS strategy recommended by European Network of Transmission System Operators (ENTSO-E).