I went ahead and got all the measurements off of various sites before I attempted this. I lost the paper I wrote the dimensions on. But this does work. I used an exacto knife, old pair of wire cutters and a file. I wish I had a dremel to do this, It would've been a lot cleaner and more exact.
I ordered an OEM Thunderbolt Extended Battery, Otterbox Defender Case, and a Zagg Screen Protector. I've been using this setup for a month now and am very pleased.
I spent $65 total on amazon.com and zagg.com for everything.
I first laid the battery in the battery cover and scored the edges. I pushed through it on one corner than began to cut. I filed down the edges. I then laid the cover in the Otterbox case and scored the outline. Then I ran the exacto back and forth for quite a while until I got through on one edge, than began to cut.
Here are my results. I know the images aren't the best quality. I haven't bought a new camera since before I've had my first android.
I peeled a bit of the padding out of the back of the Otterbox case and put it on the battery just to see how much it would push out the silicon cover, not much.
Now I am going to double-side tape the left over rectangle of the battery cover to the battery and get some weather stripping and place it on top of that.
The Zagg and the Otterbox mate well at first, eventually they begin to separate around the edges, I used the spray between them that came with the Zagg shield. The Zagg stays in place though. I haven't noticed any dust or debris since it's started. So far over this month they've stayed together in the center. I don't mind it as I am pretty hard on my phones physically and usage wise. It's hard to tell when the screen is actually on.
If you have any questions that I haven't answered, just let me know.
Thanks for looking.