hi guys, so i just got myself a used iphone 3g, the issue im having is the battery heating up quick. an example is i charged my phone overnight and in the morning i would play about 3 or 4 youtube vids and the back cover would feel really hot, ALMOST to the point where my fingers would sweat, but not THAT close to it. And sometimes i would check my phone during class time just to see if anyone texted me, not opening any apps and the phone would heat up really hot. So is this normal? i do remember the previous owner telling me he swapped the battery out to a newer one? but i can't confirm that because my battery life still sucks, dies out in close to a day. So would i need a different reliable battery? Thx in advance.