The electrical conductivity was measured for dilute electrolyte solutions of lithium perchlorate (LiClO4) in polyethylene glycols (PEG) of different molecular weights (200-600). The results were interpreted in the frame of the Stokes-Einstein-Nernst model. It was found (i) a breakdown of the model in the glycol-based polymeric matrices used and (ii) an increase of the deviation from the model predictions with increasing molecular weight of the matrix. The role of the flexibility of HO-[CH2-CH2-O](n)-H chains in the efficiency of charge carriers transport in liquid glycols is discussed.