In this research, a numerical simulation has been conducted to investigate one of the important factors for the efficient design of a maintenance-free (MF) lead-acid battery lid. Baffles and splashguards on the battery vent plug and inside the double lid are generally utilized to reduce the electrolyte loss, in the form of electrolyte droplets, during lifetime of maintenance-free batteries. Gas flow inside the battery cell and double lid is initially solved by finite volume method (FVM); then discrete phase model, in a Lagrangian reference frame, is employed to trace the electrolyte particles formed by bursting gas bubbles on the electrolyte surface and electrolyte splashing and agitating. In addition, appropriate physical models for the boundary conditions of the released gases, electrolyte droplets interaction with the lid walls and the flame arrestor are considered. (C) 2008 Elsevier B.V. All rights reserved.