Systems of lithium iodide dissolved in poly(ethylene oxide), which are prototypes of polymer electrolytes used, for example, in batteries were studied by means of molecular dynamics simulations. Investigations were aimed at the molecular driving force behind the salt uptake, the mechanism of ion transport, participation of the polymer in ion transport, ion clustering, change of polymer properties by the presence of ions, and ionic conductivity. Particular attention has been given to the differences in behavior between (previously studied) neutral and ionic species dissolved in polymers.