The voltage in LiPo (Lithium Polymer) batteries is determined based on the number of cells they have and we can easily identify this by referring to the "S" count. 

Each LiPo cell is rated at 3.7v so a 2S LiPo means it's a 2 cell battery and 7.4v, a 3S is 11.1v, 4S is 14.8v and 6S is 22.2v.