It is not very common for the battery of an electronic device to become unstable to the point of exploding, although some Apple products have suffered from this phenomenon. There are quite a few cases of explosive iPods on the net and some of the iPhone are also known.
The last case to come to light has been that of the iPhone 3GS that you see in the images and whose battery started to swell after updating to iOS 5.1 (relationship that has no logic). The owner of the terminal tried to restore his terminal without success and after leaving it in its original box, he found what you see in the images.
Fortunately, the battery did not set the iPhone case on fire because it would have been a serious problem that could have caused personal injury.
You have more images after the jump:
Source: iPhone Italy
The same thing happened to mine !! Also when updating !!
The same thing happened to my wife today but she fell apart more 🙁
The same thing happened to my old 3Gs, which had been off for about two weeks, it is charging right now, and tomorrow to buy a battery to change it!
The same thing just happened to my friend and it had been off for several days
The same thing just happened to me 10 min ago. It exploded when I was charging it. I have been stunned and it has been in the same state as the photo.