A cooling circuit with cooling liquid for lithium-ion batteries comprising a battery pack comprising a plurality of cells electrically connected with each other, suitable for powering an electric machine for traction. The cells are perimetrically delimited by external walls. At least one bag contains cooling liquid associated in contact with the outer walls of the cells. The bag is made of deformable plastic material so as to be counter-shaped to the outer walls to adhere perimetrally to the outer walls and the circuit provides forced circulation of the cooling liquid through said at least one bag.