A semi-microscopic description of ionic transport in polyethylene oxide (PEO)-type electrolytes is presented, which is based on discrete stochastic moves of individual molecular units. Diffusion coefficients for ions and for the center of mass motion of chains are calculated by Monte Carlo simulation as a function of various model parameters, with emphasis on the incorporation of pressure effects. Within an even more coarse-grained description of diffusion in an athermal system of pointlike particles and chains we provide a quantitative verification of the concept of dynamic percolation (DP).