My iPhone 5 dies and I charge it with a portable charger but It never comes on?

So my iPhone 5 dies and I get the battery screen to plug in the charger. I do so with my portable charger and leave it there. It says charging on the screen. So I come back 3 hours later and it is still on the red battery charging screen. So I assume OO just put it in the wall outlet but that doesn't work either. For some reason the only outlet that's works is the one in my room. It turns it on instantly when I get home and plug it in and when it turns on its already at 100%. I don't know what to do and it's really annoying. My iPhone is 2 years old and 16gb. Maybe it's the memory?

Most USB chargeable devices need to be plugged into either a computer USB or Portable chargers USB BEFORE it DIES. Now if it will not charge by using a wall outlet, the charging port on the phone, or the battery in the phone, needs fixing or replacing.

As for the other outlets in your home not working, may be old outlets with loose plug contacts inside the plug.

But I really don't know. I will guess that it is toast. That's why I answer questions in the AUTOMOBILE maintenance and repair category. If I knew about that stuff, I would hang out somewhere else. I do move them free of charge for those that can't figure out a simple category choice.

Try to charge it more.