3S Lipo Batteries (11.1v) are very commonly used in RC Cars & Trucks, RC Boats & RC Planes.
A LiPo Battery cell has a nominal voltage of 3.7V. For the 7.4V battery above, that means that there are two cells in series (which means the voltage gets added together). This is sometimes why you will hear people talk about a "2S" battery pack - it means that there are 2 cells in Series. So a one-cell (1S) is 3.7v, a two-cell (2S) pack is 7.4V, a three-cell (3S) pack is 11.1V, and so on.
We recommend you charge and store you battery in a Lipo Safe Bag.