Polymer electrolytes based on triblock copolymers of ethylene oxide (EO)/propylene oxide (PO)/ethylene oxide of moderate molecular weight and narrow block-length distributions, doped with M(CF3SO3)(2) and M[N(CF3SO2)(2)](2) (M = Mg, Ca, Sr and Ba), LiCF3SO3 and LiN(CF3SO2)(2) have been investigated using infrared spectroscopy, differential scanning calorimetry and conductivity measurements. The effects of varying the EO/PO block length, composition and temperature on the phase behaviour, ion-pair formation and conductivity of the polymer electrolytes have been studied. A two-phase microstructure has been observed. Ion pairing occurs for the triflate salts and the amount was found to be sensitive to the relative block sizes rather than the molecular weight of the copolymer.