The advent of new kind of superconductors can introduce a new application age. Modern magnet designs and applications push towards persistent mode system realized with multiple superconductive connected coils. The quality of field persistence is fundamental in order to characterize the goodness of the superconductive joint technical implementation. A theoretical methodology able to predict the field and the current evolution in the superconductive closed loops is necessary to introduce innovative material as MgB2 in fabrication technology and to develop robust joint techniques. ASG laboratory developed a new energetic model able to predict the ending currents of closing circuits and evaluate the persistent circuit total efficiency with short field acquisitions. This innovative model represents a powerful and flexible tool, as it is easily implementable in the study of arbitrary superconductive closed loops and applicable to complicated winding geometry. The mathematical method will be presented, and theoretical results will be compared with experimental measurements performed on specific MgB2 winding samples.