iPhone 6+ is dead and won't charge, but it says it is

In the morning I woke up, and my phone was dead. So I shrugged and left it to charge while I was at school. I came back after around 7 hours, and it still had no charge, but it said it was charging. So I moved it to another outlet, and still nothing. I tried another charger, nothing. Then I tried to plug the charger into my computer. Still nothing! I tried ANOTHER charger in ANOTHER port, and it still won’t charge. I tried taking off the case, blowing into the charging port. Nothing. So I’ve turned to the internet. My iPhone has always had a bad battery. It would drain very quickly, and when it says 30%, or something pretty low, it would just die. But I always keep it plugged in, so it’s fine. But I’m so confused, so, please help!