Liquid sloshing in partially filled tanks is a critical concern in marine, aerospace, and seismic applications, as excessive free-surface motion can generate large dynamic pressures and destabilizing wall forces. Although internal baffles are commonly used for sloshing mitigation, porous baffles exhibit inherently nonlinear flow resistance at moderate to high oscillatory velocities, an effect often neglected in linear Darcy-based models. In this work, sloshing dynamics in a two-dimensional rectangular tank equipped with multiple vertical porous baffles are investigated using the Scaled Boundary Finite Element Method (SBFEM), with a nonlinear Darcy–Forchheimer-type porous boundary condition imposed along the baffles. The semi-analytical nature of SBFEM enables efficient treatment of wave-dominated flow while naturally accommodating domain subdivision induced by multiple baffles. A robust iterative algorithm is developed to incorporate the nonlinear porous resistance along the baffle interfaces within the SBFEM framework. The proposed formulation is validated against published solutions based on the matched eigenfunction expansion method (MEEM) for tanks with single and double porous baffles, demonstrating excellent agreement. A systematic parametric study is then carried out to examine the coupled influence of baffle porosity, baffle depth, spacing between baffles, and excitation amplitude on the free-surface elevation and sloshing-induced wall forces. The results reveal pronounced amplitude-dependent dissipation and non-monotonic frequency responses arising from nonlinear flow resistance and inter-compartment coupling. In particular, intermediate porosity and spacing configurations are shown to provide optimal sloshing attenuation by balancing energy transmission and nonlinear dissipation, while excessively deep or closely spaced baffles can promote localized high-frequency resonances. The present study highlights the importance of nonlinear porous boundary conditions in accurately capturing sloshing behavior in multi-baffle systems and establishes SBFEM as an efficient and physically consistent framework for analyzing sloshing control strategies under realistic operating conditions.