Solid Polymer Electrolytes (SPEs) are key-enabling alternatives to liquid/gel electrolytes of Lithium-ion Batteries paving the way toward safer-by-design and higher energy density solid-state batteries by leveraging Li metal and high voltage (e.g. NCM and NCA) negative and positive electrode materials. In this communication, we discuss how polyester-based SPEs, specifically the two poly(n-pentyl maleate) (PPM) and poly(n-pentyl fumarate) (PPF) stereoisomers, owing to their superior Li+ transference number (tLi+) and oxidation resistance, can surpass poly(ethylene oxide) (PEO)-based SPEs. We demonstrate that PPM/LiTFSI and PPF/LiTFSI exhibit (i) respective tLi+ values up to 0.78 and 0.73 at 80 °C, i.e. >7 times higher than the one of PEO/LiTFSI (~ 0.10) and (ii) ionic conductivity up to 0.1 mS cm-1 at 80 °C for PPM/LiTFSI, i.e. > 3.5 times higher than that of PPF/LiTFSI.