In lithium batteries, a porous separator filled with an electrolyte is placed in between the electrodes. Properties of the separator such as porosity and wettability strongly influence the conductivity of the electrolyte-separator composite. This study focuses on three commercial separators: a single layer polypropylene (Celgard 2500), a trilayer polypropylene-polyethylene-polypropylene (PP-PE-PP), and a porous polytetrafluoroethylene (PTFE). Electron microscopy was used to characterize the pore structure, and these experiments reveal large differences in pore morphology. The separators were soaked in both carbonate- and perfluoropolyether-based electrolytes. The conductivity of the neat electrolytes (sigma(0)) varied from 6.46 x 10(-6) to 1.76 x 10(-2) S cm(-1). The porosity and wettability of the separator affect the electrolyte uptake that in turn affect the conductivity of electrolyte-separator composites. The conductivity of the electrolyte-separator composites (sigma) was found to follow a master equation, sigma = 0.51. sigma(0).phi(3.2 +/- 0.2)(c), where phi(c) is the volume fraction of the electrolyte in each separator. (C) 2016 Elsevier B.V. All rights reserved.