Excuse me, Tartarus, I've done it myself and have given feedback, and it actually has worked. I was panicing after my iPhone not charging above 25% for a whole night after a lightning storm.. thought the storm itself had broken my Phone.
The trick has worked and the scientific explanation behind it sounds very logical.
Try it yourself, 50*C heat to the back of your phone will not damage it. Monitor how much you heat it up.
It's nothing to do with Apple, it's directed at how a Li-ion battery functions.
No idea why anyone would want to maliciously destroy other peoples iPhones over the internet.
Edit:
"Your device is designed to perform well in a wide range of ambient temperatures, with 62? to 72? F (16? to 22? C) as the ideal comfort zone. It’s especially important to avoid exposing your device to ambient temperatures higher than 95? F (35? C), which can permanently damage battery capacity. That is, your battery won’t power your device as long on a given charge. Charging the device in high ambient temperatures can damage it further. Even storing a battery in a hot environment can damage it irreversibly. When using your device in a very cold environment, you may notice a decrease in battery life, but this condition is temporary. Once the battery’s temperature returns to its normal operating range, its performance will return to normal as well."
What is this garbage..? If this is true, how in the world am I to charge my iPhone in Australia? 35*C ambience? It gets to 45*C here! ':f
P.S. the heating I believe is only supposed to be only 60 seconds tops, I don't think I'd go with the water heater idea.. that's too long and the plastic elements might warp.