Warranty??

Here's the story, me and a friend bought the Samsung galaxy s 4 at the same time, we both had battery problems with the phone, so Samsung replaced it because it was a faulty batch, keep in mind I think that the initial battery overheating to the point where it started to burn your hand and you couldn't hold the device is what I think caused all this, but carrying on, my friends phone starts rebooting all the time and he takes it in, no problem, mine starts rebooting one week later all the time, just a loop reboot and then all of a sudden \warranty doesn't cover your phone"so I mentioned about my friends phone and apparently my phone has a crack on the screen"