Abstract: High Power battery packs are a series/parallel connection of single energy storage cells.The series connection of cells affects in the whole battery pack energy and power due to the unbalancing behavior of each different cell. To improve the whole battery pack energy a balancing system is connected. Passive balancing systems are wasteful and do not increase the Battery pack energy during discharge. Active balancing systems are efficient but most topologies add big complexity to the BMS work. Single switch active balancing systems are simple and reliable. During this work the main balancing current modelling and efficiency equations are presented for the most important single switch active balancing systems. These expressions permit to evaluate the balancing power of the system, and to know how much energy is balanced during the balancing system process between the Weak cell and the Strong cells. Experimental validation of each balancing system is implemented to compare balancing power, efficiency and behavior.