The autonomous system comprises an intermittent power source delivering a direct current. A supercapacitance is connected in parallel with the battery and the power source respectively via a first switch and a second switch. Charging of the battery comprises pulsed current charging managed by a control circuit. During a current pulse, the amplitude of the current and the amplitude of the voltage increase at the terminals of the battery are measured. The dynamic internal resistance of the battery is determined from said amplitudes. A maximum acceptable current threshold is determined according to a maximum voltage threshold, to said dynamic internal resistance and to the no-load voltage at the battery terminals. At the next current pulse, the value of the charging current is limited by controlling the closing time of the second switch.