Representing polyether-salt systems by chains of interacting coordination shells, defined by the cation and by its nearest ligands, we derive the interaction potential between closest shells - the inter-shell potential - in terms of two-electron polarization effects. Values are presented for monovalent-based crystalline poly(ethylene oxide), PEO, electrolytes. For the eutectic composition PEO 1 2 EuBr 3 , the inter-shell energy is evaluated also by relating the empirical value of the nearest-ligands local-field potential with the variation of the Eu 3 + concentration. Both methods give the same results.