The impact of a Battery Energy Storage System (BESS) on the dynamic properties of an isolated power system will be analyzed in this paper. An isolated power system involving a BESS is modelled using the MATLAB/Simulink package, which includes the essential controls for the generators and the BESS. Various types of dynamic disturbances are applied to the system, with and without the presence of BESS. By comparing the system responses, the influence of the BESS during the dynamic disturbances is discovered. The simulation results indicate that the BESS is able to mitigate the negative effects of dynamic disturbances so that the stability of the power system is enhanced. However, it is also observed that the BESS might introduce an unexpected temporary degradation in the power quality. Therefore, to ensure the advantages of a BESS outweigh the disadvantages, critical assessments are necessary before a BESS can be employed on an isolated power system.