I find it both amusing and telling that that is the only possibility you consider. Perhaps there was a manufacturing flaw in the battery, or it was damaged by dropping, yet 'blame the user' seems to be your knee-jerk reaction.

I started this by saying "Perhaps" the phone was jailbroken. I don't assume that is the case, I just provide it as a plausible option. Also notice that the Apple logo on the phone back has been modified.