A method for estimating the state of charge (SoC) of an electrochemical element, comprising: - initiating an operation of charging or discharging the electrochemical element that is traversed by a current; - during the operation of charging or discharging the electrochemical element: -- an operation of charging or discharging a power storage element that is traversed by the same current as the electrochemical element, the power storage element having a voltage/charge level relationship that is bijective for at least two values of the voltage at the terminals of the storage element, the capacity CES of the storage element representing a portion of the total capacity of the electrochemical element; -- detecting that the storage element is charged or discharged; -- computing a new value of the capacity CN of the electrochemical element by means of the formula: --- for a charging operation: C N = C N − 1 + C ES; --- for a discharging operation: C N = C N − 1 − C ES; where C N-1 is a previous known value of the capacity of the electrochemical element, characterized in that the method further comprises: - following the detection that the storage element is charged or discharged, a polarity inversion at the terminals of the storage element causing discharging of the storage element if the storage element is charged and charging of the storage element if the storage element is discharged; - an iteration of the charging or discharging of the storage element, the detection and the computing. - initiating an operation of charging or discharging the electrochemical element that is traversed by a current; - during the operation of charging or discharging the electrochemical element: -- an operation of charging or discharging a power storage element that is traversed by the same current as the electrochemical element, the power storage element having a voltage/charge level relationship that is bijective for at least two values of the voltage at the terminals of the storage element, the capacity CES of the storage element representing a portion of the total capacity of the electrochemical element; -- detecting that the storage element is charged or discharged; -- computing a new value of the capacity CN of the electrochemical element by means of the formula: --- for a charging operation: C N = C N − 1 + C ES; --- for a discharging operation: C N = C N − 1 − C ES; -- an operation of charging or discharging a power storage element that is traversed by the same current as the electrochemical element, the power storage element having a voltage/charge level relationship that is bijective for at least two values of the voltage at the terminals of the storage element, the capacity CES of the storage element representing a portion of the total capacity of the electrochemical element; -- detecting that the storage element is charged or discharged; -- computing a new value of the capacity CN of the electrochemical element by means of the formula: --- for a charging operation: C N = C N − 1 + C ES; --- for a discharging operation: C N = C N − 1 − C ES; --- for a charging operation: C N = C N − 1 + C ES; --- for a discharging operation: C N = C N − 1 − C ES; - following the detection that the storage element is charged or discharged, a polarity inversion at the terminals of the storage element causing discharging of the storage element if the storage element is charged and charging of the storage element if the storage element is discharged; - an iteration of the charging or discharging of the storage element, the detection and the computing.