NOVELTY - Biaxially oriented polyester film comprises polyester, and at least one hydrolysis stabilizer including a glycidyl ester of a branched 5-50C monocarboxylic acid, where the hydrolysis stabilizer is present in the film in the form of its reaction product with at least some of the end-groups of the polyesters, the polyester film further comprises a metal cation including group I metal cation or group II metal cation, and the reaction product is obtained by the reaction of the hydrolysis stabilizer with the end-groups of the polyester in the presence of the metal cations.    USE - The biaxially oriented polyester film is useful as: a white film, a black film or an opaque film; and a layer in a photovoltaic cell (all claimed).    ADVANTAGE - The biaxially oriented polyester film: The polyester film: exhibits an elongation to break, measured according to ASTM D882, of at least 10% after at least 56 (preferably at least 92) hours when aged at 121 degrees C and 1.2 bar pressure; exhibits improved haze (of not greater than 30%), and/or total luminous transmission (of at least 50%); exhibits improved hydrolysis resistance; is manufacture without the evolution of toxic by-products and in economical manner without increasing the film breakage; has no odor detected around the film die; exhibits reduced levels die-lines and profile defects; is self-supporting film, thus capable of existing independently in the absence of a supporting base; exhibits improved windability, uniformity and quality when compared to conventional films; exhibits high intrinsic property and good processability; and improved mechanical and/or optical properties.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a photovoltaic cell comprising a front-plane, electrode layers, a photovoltaic-active layer, and a back-plane, where the front-plane and/or back-plane comprises the film;    (2) manufacturing biaxially oriented polyester film, comprising extruding a layer of molten polyester and the hydrolysis stabilizer, which is present in the extrudate in the form of its reaction product with at least some of the end-groups of the polyester, where the reaction product is obtained by the reaction of the hydrolysis stabilizer with the end-groups of the polyester in the presence of the metal cations, quenching the extrudate, stretching the quenched extrudate in two mutually perpendicular directions, and heat-setting the film, which is stabilized at 200-225 degrees C;    (3) improving the hydrolysis resistance of a biaxially oriented polyester film, comprising reacting the polyester with the hydrolysis stabilizer; and    (4) the use of the metal cations for improving the hydrolysis resistance of the film comprising the hydrolysis stabilizer.