Automatic method for estimating the state of charge of a cell of a battery, this method including: a) acquiring, at an instant k, a measured value y k of the voltage across the terminals of the cell, and a measured intensity i k of the current charging or discharging the cell; and b) estimating (166; 246) a capacity C n,k3 of the cell at an instant k3, this capacity C n,k3, which is expressed in Ah, representing the maximum amount of electrical energy storable in the cell at the instant k3, the instant k3 being the instant at which the capacity C n,k3 has been estimated closest the instant k, and the instants k3 being less frequent than the instants k, this estimation including: calculating a prediction of the capacity C n,k3 using a state model that relates the capacity C n,k3 to the capacity C n,k3-1 of the same cell at a preceding instant k3-1, then correcting the prediction of the capacity C n,k3 depending on a measured intensity, at the instant closest the instant k3, of the current charging or discharging the cell; and c) estimating the state of charge SOCk of the cell, at the instant k, from the measured value y k, from the measured intensity i k and from the capacity C n,k3 of the cell; characterized in that the correction of the prediction of the capacity C n,k3 includes: - acquiring, at the instant k3, a measurable physical quantity z k3 defined by the following relationship: where k is the instant closest the instant k3 and N is an integer higher than or equal to z k 3 = ∑ m = k − N m = k − 1 i m one, z k3 being equal to i k-1 when N is equal to 1; - calculating a prediction ẑ k3 of the measurable physical quantity z k3 using the following observation model: z ^ k 3 = SO C k − SO C k − N NT e.3600. C n, k 3 where: - k is the instant closest the instant k3, - SOC k-N is the state of charge of the cell at the prior instant k-N, and - C n,k3 is, in this observation model, the prediction of the capacity of the cell at the instant k3, i.e. that calculated just before being corrected; and - correcting the prediction of the capacity C n,k3 depending on the difference between the acquired physical quantity z k3 and the prediction ẑ k3 calculated from the observation model. a) acquiring, at an instant k, a measured value y k of the voltage across the terminals of the cell, and a measured intensity i k of the current charging or discharging the cell; and b) estimating (166; 246) a capacity C n,k3 of the cell at an instant k3, this capacity C n,k3, which is expressed in Ah, representing the maximum amount of electrical energy storable in the cell at the instant k3, the instant k3 being the instant at which the capacity C n,k3 has been estimated closest the instant k, and the instants k3 being less frequent than the instants k, this estimation including: calculating a prediction of the capacity C n,k3 using a state model that relates the capacity C n,k3 to the capacity C n,k3-1 of the same cell at a preceding instant k3-1, then correcting the prediction of the capacity C n,k3 depending on a measured intensity, at the instant closest the instant k3, of the current charging or discharging the cell; and c) estimating the state of charge SOCk of the cell, at the instant k, from the measured value y k, from the measured intensity i k and from the capacity C n,k3 of the cell; - acquiring, at the instant k3, a measurable physical quantity z k3 defined by the following relationship: where k is the instant closest the instant k3 and N is an integer higher than or equal to z k 3 = ∑ m = k − N m = k − 1 i m one, z k3 being equal to i k-1 when N is equal to 1; - calculating a prediction ẑ k3 of the measurable physical quantity z k3 using the following observation model: z ^ k 3 = SO C k − SO C k − N NT e.3600. C n, k 3 where: - k is the instant closest the instant k3, - SOC k-N is the state of charge of the cell at the prior instant k-N, and - C n,k3 is, in this observation model, the prediction of the capacity of the cell at the instant k3, i.e. that calculated just before being corrected; and - correcting the prediction of the capacity C n,k3 depending on the difference between the acquired physical quantity z k3 and the prediction ẑ k3 calculated from the observation model. - k is the instant closest the instant k3, - SOC k-N is the state of charge of the cell at the prior instant k-N, and - C n,k3 is, in this observation model, the prediction of the capacity of the cell at the instant k3, i.e. that calculated just before being corrected; and - correcting the prediction of the capacity C n,k3 depending on the difference between the acquired physical quantity z k3 and the prediction ẑ k3 calculated from the observation model.