The problem with extended batterys is that most of them work by being bigger than the original battery. The casing on the note2 is pretty much as close as it can be, so there isn't much space to get a larger battery in there, so anything that fits in the standard cover isn't going to be much bigger.
If not making your device bigger is a dealbreaker for you, your best option is to buy several standard batterys and swap them when they run out (remembering to charge them when you get a chance)