Due to high penetrations of renewable energy systems (RESs), deployment of energy storage is significantly increased in recent years. Among varieties of energy storage options, battery energy storage systems (BESSs) are getting popular as they provide reliable performance with low-inertia RESs. Although BESS smooth out RES energy, they can negatively influence low-frequency oscillations of power systems due to inertia-less characteristics. However, a very scant attention has been paid to understand the BESS impact on low frequency oscillation of power systems. Hence, this paper investigates the impact of BESSs on the low-frequency oscillation. In order to analyse the impact of BESS's control and its dynamic interaction, a single machine infinite bus, popularly known as “Philip-Heffron model” is used. Eigenvalue, nonlinear time domain simulation and participation factor analyses are used to examine system's behaviours with BESS. From simulation results, it is found that the gain of BESS's controller changes the dynamic behaviour of synchronous machines and optimally tuned gain can enhance system's damping.