[_petronius]

Although I really like my Nexus 4 as a piece of hardware (generally, it just works) I have run into this problem before. Some googling around the issue indicates that it's fairly common, and may be related to the way the device does a poor job of offloading heat. (Due to the arrangement of the internals, a lot of the heat conducts back through the battery connector instead of into the case of the phone, shortening the lifetime of the battery, or so I read somewhere.)

The heat sink issue can apparently be relieved[1], although I haven't tried this on my own device yet. I did replace the battery, though, after the first one failed and started swelling (not as badly as the pictures, but bad enough to deform the back case noticeably).

[1]: http://www.makeuseof.com/tag/got-a-hot-nexus-4-heres-a-hack-...