Installation (100; 100′) comprising two batteries joined in parallel with the aid of a first device (1; 1′) for protection of a voltage source (10; 20), comprising: a parallel assembly comprising a controlled breaker (5; 52, 53) and a resistive element (4; 42, 43), a coil (3) arranged in series with the said assembly between, the two batteries, a means (6) of control of the breaker of the said assembly controlled as a function of the voltage difference (V_AB) between the two batteries so that the controlled breaker is closed when the voltage difference becomes less than a first threshold (threshold 1) and that the controlled breaker is open when the voltage difference becomes greater than a second threshold (threshold 2).