Composite polymer electrolytes (CPE), comprising poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), aluminum oxyhydroxide, (AlO[OH] (n) - of 40 nm and 7 mu m) as filler and LiN(C2F5SO2)(2) or LiClO4 as lithium salt were prepared using a solution casting technique. The membranes were subjected to XRD, impedance spectroscopy, compatibility and transport number studies. The incorporation of nanofiller greatly enhanced the ionic conductivity and the compatibility of the composite polymer electrolyte. The electrochemical properties of CPE with nano sized fillers are better than those of micron size. Charge- discharge studies of Li Cr0.01Mn1.99O4/CPE/Li cells were made at 70 degrees C and are discussed.