I don't know if your phone is defective or not, but 113F is the maximum recommended charging temperature. (140F is the maximum recommended discharging temperature.) Charging at 118F may shorten the battery life a little, but it shouldn't be dangerous. But wait to see if people with the M8 post with high charging temperatures too (which means a bad design), or not (which means a bad phone or battery). OR - if you're charging in a really hot car, with no air flow around the phone, it's going to overheat, since it can't get rid of the heat it's generating by charging. (Anything over about 90F is going to impede cooling - but if it's that hot in the car, you're probably running the AC, so get a mount that holds the phone in front of the AC vent and that will keep it cool.)