Use of a polymeric-inorganic nanoparticle composition as a heat transfer fluid in battery or other electrical equipment systems, wherein the polymeric-inorganic nanoparticle composition is obtainable by milling a mixture, the mixture comprising one or more inorganic nanoparticle compound and one or more polymer compound, wherein the one or more inorganic nanoparticle compound is selected from the group consisting of metal or metalloid oxide nanoparticle, metal or metalloid nitride nanoparticle, metal or metalloid carbide nanoparticle, or a mixture thereof, and wherein the one or more polymer compound is obtainable by polymerizing a monomer composition comprising: a) 1 to 35 % by weight, based on the total weight of the monomer composition, of one or more functional monomer selected from the list consisting of: a1) aminoalkyl (meth)acrylates and aminoalkyl (meth)acrylamides; a2) nitriles of alkyl (meth)acrylic acid and other nitrogen-containing alkyl (meth)acrylates; a3) (meth)acrylates of ether alcohols; a4) oxiranyl alkyl (meth)acrylate; a5) phosphorus-, boron- and/or silicon-containing alkyl (meth)acrylates; a6) heterocyclic alkyl (meth)acrylates; a7) vinyl halides; a8) vinyl esters; a9) vinyl monomers containing aromatic groups; a10) heterocyclic vinyl compounds; a11) vinyl and isoprenyl ethers; a12) methacrylic acid and acrylic acid, b) 65 to 99% by weight of one or more alkyl (meth)acrylate monomer, wherein each of the alkyl group of the one or more alkyl (meth)acrylate monomer is independently linear, cyclic or branched and comprises from 1 to 40 carbon atoms, based on the total weight of the monomer composition, and wherein the weight ratio of the one or more inorganic nanoparticle compound to the one or more polymer compound is 9:1 to 1:5. wherein the one or more inorganic nanoparticle compound is selected from the group consisting of metal or metalloid oxide nanoparticle, metal or metalloid nitride nanoparticle, metal or metalloid carbide nanoparticle, or a mixture thereof, and wherein the one or more polymer compound is obtainable by polymerizing a monomer composition comprising: a) 1 to 35 % by weight, based on the total weight of the monomer composition, of one or more functional monomer selected from the list consisting of: a1) aminoalkyl (meth)acrylates and aminoalkyl (meth)acrylamides; a2) nitriles of alkyl (meth)acrylic acid and other nitrogen-containing alkyl (meth)acrylates; a3) (meth)acrylates of ether alcohols; a4) oxiranyl alkyl (meth)acrylate; a5) phosphorus-, boron- and/or silicon-containing alkyl (meth)acrylates; a6) heterocyclic alkyl (meth)acrylates; a7) vinyl halides; a8) vinyl esters; a9) vinyl monomers containing aromatic groups; a10) heterocyclic vinyl compounds; a11) vinyl and isoprenyl ethers; a12) methacrylic acid and acrylic acid, b) 65 to 99% by weight of one or more alkyl (meth)acrylate monomer, wherein each of the alkyl group of the one or more alkyl (meth)acrylate monomer is independently linear, cyclic or branched and comprises from 1 to 40 carbon atoms, based on the total weight of the monomer composition, a) 1 to 35 % by weight, based on the total weight of the monomer composition, of one or more functional monomer selected from the list consisting of: a1) aminoalkyl (meth)acrylates and aminoalkyl (meth)acrylamides; a2) nitriles of alkyl (meth)acrylic acid and other nitrogen-containing alkyl (meth)acrylates; a3) (meth)acrylates of ether alcohols; a4) oxiranyl alkyl (meth)acrylate; a5) phosphorus-, boron- and/or silicon-containing alkyl (meth)acrylates; a6) heterocyclic alkyl (meth)acrylates; a7) vinyl halides; a8) vinyl esters; a9) vinyl monomers containing aromatic groups; a10) heterocyclic vinyl compounds; a11) vinyl and isoprenyl ethers; a12) methacrylic acid and acrylic acid, a1) aminoalkyl (meth)acrylates and aminoalkyl (meth)acrylamides; a2) nitriles of alkyl (meth)acrylic acid and other nitrogen-containing alkyl (meth)acrylates; a3) (meth)acrylates of ether alcohols; a4) oxiranyl alkyl (meth)acrylate; a5) phosphorus-, boron- and/or silicon-containing alkyl (meth)acrylates; a6) heterocyclic alkyl (meth)acrylates; a7) vinyl halides; a8) vinyl esters; a9) vinyl monomers containing aromatic groups; a10) heterocyclic vinyl compounds; a11) vinyl and isoprenyl ethers; a12) methacrylic acid and acrylic acid, b) 65 to 99% by weight of one or more alkyl (meth)acrylate monomer, wherein each of the alkyl group of the one or more alkyl (meth)acrylate monomer is independently linear, cyclic or branched and comprises from 1 to 40 carbon atoms, based on the total weight of the monomer composition,