I know it sounds like bs but it just happened to my 64gb 6 plus while I was charging it (via PC USB to be specific). I started charging it at 50%, then I left it on my desk. After 2 hours later, I found the phone is really hot and the battery level is down to 38% . I know it sounds like some app is running hot so I checked the battery usage immediately, only found Whatsapp at 32% and Home & Lock screen at 11%, and other apps at less than 10%. Nothing was uploading (ie. Dropbox, iCloud, etc.). This is 1st time happened since I've owned the original iPhone and I have charging with PC USB since all the time. Has anyone else experienced this before? do I have a bad device?