Systems and methods are herein disclosed for efficiently and cost-effectively balancing the voltages across batteries and/or cells in an energy storage system. A controller monitors the battery voltages and instructs regulator circuits to balance voltages between any batteries or sets of batteries having imbalanced voltages. Regulator circuits implementing a modified Ćuk converter can be utilized. Regulator circuits can have two capacitive circuits, one inductive circuit, and two switches. Two capacitors, an inductor, and two field effect transistors can be used in each regulator circuit.