Mugen Power Extended Battery w/ Battery Cover for Samsung Galaxy S II Skyrocket i727, Black Mugen Power Extended Battery w/ Battery Cover for Samsung Galaxy S II Skyrocket i727 3,800mAh, 3.7V power rating; Lithium-ion technology Provides more than double the capacity of the standard battery; Supports NFC functionality Comes with an extended battery cover door that accommodates the extended battery and features a built-in kickstand Adds approximate 7mm in thickness; Keeps your phone charged and ready to go, even with heavy phone and data usage