Li-Polymer batteries are the newest available batteries for airsoft and other hobby toys. They are designed as a light weight, high output power source. This 11.1v Li-Po battery can deliver more power than 12v Ni-MH large type battery with only half of the size and a third of the battery cells. 

Note: it is always recommend to double check and the battery pack dimensions with the your gun's battery compartment to make sure it fits.