Method for the serial connection of additional sources of direct current to equalize the voltage level in a system when the load is increased. It includes the following steps: by means of wires, a first load is plugged in between the positive and negative terminals of the original source of direct current, observing polarity. In addition, one of the wires, connected to the negative terminal of the original source of direct current is the common negative wire, while the second wire, connected to the positive terminal of the original source of direct current, is the common positive wire.