A battery made up of nickel-cadmium electrochemical storage cells including an indicator of a state of charge, the indicator comprising - sensors (20; 30; 40) for performing continuous measurements of voltage and current and of temperature of said battery, - means for determining at a time t, a history (H T) for charge/discharge of said battery based on said measurements - data storage means in which there are stored at least a history (H R) of charge/discharge, a predefined reference voltage (U R), current (I R) and temperature (T R), and the measurements and history determined (H T) - a control unit for - measuring a voltage (U T), a current (I T) and a temperature (T T) of said battery at a time t, - determining an operation mode (Ch; D; R) of said battery by comparing the voltage (U T) and current (I T) measured at a time t, with respectively a reference voltage and reference current (I R), - determining a correction to be applied to the voltage (U T) and current (I T) measured at time t by comparing the temperature (T T) measured at time t, with a reference temperature (T R), - calculating a theoretically available capacity (CT AVAIL) of said battery depending on the operating mode (Ch, D, R) and the correction, as well as a voltage (U T) and a current (I T) measured at time t, - determining a need for recalibration (R C) of the theoretically available capacity (CT AVAIL) of the battery by comparing said history (H T) determined at time t to the reference history (H R), - depending on the need for recalibration (R C) and the theoretically available capacity, calculating a capacity actually available (CR AVAIL) of said battery, - based on said capacity actually available (CR AVAIL), defining the state of charge of said battery, - a device for displaying said defined state of charge. - sensors (20; 30; 40) for performing continuous measurements of voltage and current and of temperature of said battery, - means for determining at a time t, a history (H T) for charge/discharge of said battery based on said measurements - data storage means in which there are stored at least a history (H R) of charge/discharge, a predefined reference voltage (U R), current (I R) and temperature (T R), and the measurements and history determined (H T) - a control unit for - measuring a voltage (U T), a current (I T) and a temperature (T T) of said battery at a time t, - determining an operation mode (Ch; D; R) of said battery by comparing the voltage (U T) and current (I T) measured at a time t, with respectively a reference voltage and reference current (I R), - determining a correction to be applied to the voltage (U T) and current (I T) measured at time t by comparing the temperature (T T) measured at time t, with a reference temperature (T R), - calculating a theoretically available capacity (CT AVAIL) of said battery depending on the operating mode (Ch, D, R) and the correction, as well as a voltage (U T) and a current (I T) measured at time t, - determining a need for recalibration (R C) of the theoretically available capacity (CT AVAIL) of the battery by comparing said history (H T) determined at time t to the reference history (H R), - depending on the need for recalibration (R C) and the theoretically available capacity, calculating a capacity actually available (CR AVAIL) of said battery, - based on said capacity actually available (CR AVAIL), defining the state of charge of said battery, - measuring a voltage (U T), a current (I T) and a temperature (T T) of said battery at a time t, - determining an operation mode (Ch; D; R) of said battery by comparing the voltage (U T) and current (I T) measured at a time t, with respectively a reference voltage and reference current (I R), - determining a correction to be applied to the voltage (U T) and current (I T) measured at time t by comparing the temperature (T T) measured at time t, with a reference temperature (T R), - calculating a theoretically available capacity (CT AVAIL) of said battery depending on the operating mode (Ch, D, R) and the correction, as well as a voltage (U T) and a current (I T) measured at time t, - determining a need for recalibration (R C) of the theoretically available capacity (CT AVAIL) of the battery by comparing said history (H T) determined at time t to the reference history (H R), - depending on the need for recalibration (R C) and the theoretically available capacity, calculating a capacity actually available (CR AVAIL) of said battery, - based on said capacity actually available (CR AVAIL), defining the state of charge of said battery, - a device for displaying said defined state of charge.