I just noticed that charging from the usb to the outlet that the outlet causes the iphone to heat up way more then the usb does. The usb stays a pretty constant lukewarm feel while the outlet the first maybe 20 minutes was 3 times warmer but then towards the end of the charging cycle it cooled down to about the level of a usb. It this just because the usb charges at a slower pace then compared to the outlet charing it faster cause it to heat up more then the usb? Anyone experience this? Most of the past phones I've owned never heated up, not unless you used it while it was charging which i haven't with this phone.