Humbucker pickups in a Strat?

Ok so I want to put two humbucker pickups in a Strat I want to mod. Can someone please explain the whole 9 volt battery thing? I understand why it's used but just how much room has to be made for the battery to fit and how many other complications may I have to deal with that I havent thought of yet? There most likely going to be EMG humbuckers as well. Thanks for any information you can give me on this project.