ok so i was looking at my side grip and was pretty sure i could fit two batteries in it... my biggest concern was that i would blow through the material and leave big holes in the grip...

so the first thing i did was take off the felt strip on the inside of the grip and the rubber fake leather on the outside...

to my surprise i found 4 screws..... so ... I unscrewed them... and found that the side grip was hollow probably to save on weight



next i took the biggest drill bit i had and drilled through the middle piece and filed down all the sides all the way to the edge but keeping enough material on it so it doesn't deform.... i periodically checked clearance of the battery and filed away a little bigger than the battery... it's a good idea to tape up the grip so it doesnt get scratched in the process of drilling...



next i rescrewed on the front plate and added some gaffer tape inside the hole so the battery doenst' ground itself on the grip



put gaffer tape on top to keep the batteries in the hole and to shield the camera body from the grip



next i super glued the rubber leatherette back on the grip

here's what it looks like on the camera... you can't even tell batteries are there... all in all it took about 45minutes to do.. and now i'll NEVER be without spares...