Method for determining the operating temperature of a cell of an electric charge accumulator assembly, particularly for electric or hybrid vehicles, which comprises the steps of: - providing a reference model of a cell, representative of the evolution over time of a relationship between the internal electrical resistance of the cell and the cell temperature, depending on the state of charge; - determining the real internal electrical resistance of a cell of an accumulator assembly; - estimating the state of charge of said cell; - estimating the ageing of said cell; and - determining an estimated operating temperature of said cell from the determined value of the real internal electrical resistance of said cell and the estimated state of charge, depending on the degree of ageing of the cell, by comparison with said reference model, characterized in that said comparison with the reference model includes the recursive operations of: - estimating a value of the internal electrical resistance of said cell from a determined state of charge of the cell and from an estimate of temperature of the cell, according to said reference model; - comparing said estimated value of the internal electrical resistance of the cell with the determined value of the real internal electrical resistance of the cell; and - correcting the estimate of the temperature of the cell as a function of the difference between said estimated value of the internal electrical resistance of the cell and said determined real value of the internal electrical resistance of the cell, wherein the method comprises calculating the real internal electrical resistance of the cell as a function of the variation of current through the cell in a sampling period, so that if this variation is greater than a predetermined threshold the real internal electrical resistance of the cell is calculated as the ratio between the voltage differential and the current differential during the aforementioned sampling period, and if this variation is lower than said predetermined threshold, the real internal electrical resistance of the cell is estimated to be unchanged compared to the value calculated in a previous sampling period. - providing a reference model of a cell, representative of the evolution over time of a relationship between the internal electrical resistance of the cell and the cell temperature, depending on the state of charge; - determining the real internal electrical resistance of a cell of an accumulator assembly; - estimating the state of charge of said cell; - estimating the ageing of said cell; and - determining an estimated operating temperature of said cell from the determined value of the real internal electrical resistance of said cell and the estimated state of charge, depending on the degree of ageing of the cell, by comparison with said reference model, - estimating a value of the internal electrical resistance of said cell from a determined state of charge of the cell and from an estimate of temperature of the cell, according to said reference model; - comparing said estimated value of the internal electrical resistance of the cell with the determined value of the real internal electrical resistance of the cell; and - correcting the estimate of the temperature of the cell as a function of the difference between said estimated value of the internal electrical resistance of the cell and said determined real value of the internal electrical resistance of the cell,