This paper presents and analyzes a non-dissipative balancing system for supercapacitors. The circuit design is carried out by means of a controlled buck-boost converter in order to have the same voltage in each supercapacitor. The paper presents an energy loss analysis in two cases: a dissipative and a non-dissipative balancing circuit. It also develops a probabilistic analysis in order to estimate the efficiency of the balancing system during a constant current charge for a 10-, 30- and 45-supercapacitor series stack. Finally, simulations and measurements are carried out to verify efficiency in a supercapacitor stack with the buck-boost topology. The prototype on which the balancing analysis is performed consists of 45 3000F supercapacitors, and stacks of up to 60 devices are simulated.