The Galaxy Nexus extended 2100mah battery fits into the Galaxy SII skyrocket (which is shipped with a 1850mah battery) but some users have had a hard time closing their skyrocket's back covers due to the extra thickness of the extended battery. I demonstrate in this instructable an easy way to trim the battery to fit the Skyrocket with no back cover problems.
See this XDA thread for the original discussion: http://forum.xda-developers.com/showthread.php?t=1528782
The Nexus extended battery is available online and at Verizon stores for $25. I purchased from Verizon in order to be certain I was receiving an OEM battery.
Step 1: Tools Required
The only tool required is a razor knife. I used an x-acto knife but a razor blade would also work.
This picture shows how much material I removed during the modification.
Step 2: Trim the Back Side of the Battery
The high areas on the battery that cause problems with the back cover are mainly around the edges of the battery. I carefully trimmed a very small amount of black plastic from the very edge, as is visible in the photo. I also trimmed the metallic sticker away from the raised edge. Trimming the high spots and cutting back the sticker allow the battery to sit deeper in the phone.
Don't use the battery as a cutting board. Instead, peel back the battery a bit and slice it without touching the battery body.
Step 3: Trim the Front Side of the Battery
With the battery sitting deeper in the phone, your cover may snap into place with no more modification needed. If your back cover still will not close along the left side of the phone you can trim the high spot on the plastic on the very top left corner of the battery and reduce thickness even more by trimming the sticker.
Some have removed the sticker altogether, but I wanted to take off the minimum amount of material possible. The left side of the battery (from the perspective of the photos below) is where the sticker overlaps. Along that left side, which is closest to the cover snaps, the overlap adds to the overall thickness of the sticker. Most phones' covers will not snap closed along this side of the phone. I have pointed to the edge of the overlapping area with the knife in a picture below, but this was taken after I trimmed it.
In order to reduce thickness while leaving the battery looking as intact as possible I first peeled back the sticker revealing the NFC chip. With the visible part of the sticker peeled back, I was able to then access the edge of the sticker it covered. Peel this edge back and cut it with your knife so that the sticker edges no longer overlap. I was not very neat with my cut. If you scribe a light line using your knife along the edge you will cut using the top edge as a guide you will be able to follow that line and make a straight clean cut.
Do not use the battery as a cutting board when you trim the sticker. Peel the sticker back and slice it.
Step 4: Finished Result
With the trimmed battery installed, the back cover snaps into place with no gaps. There is still a slight bulge at the top of the battery which I tried to capture using the reflection from my lamp. This bulge is not noticeable in normal use and is only barely detectable if you really look for it.
Enjoy your extra battery life, heavier feel, and tighter battery compartment.