Why does my iphone use up battery faster than it charges, as it is charging?

Why does my iphone use up battery faster than it charges, as it is charging?

Added (1). It is an iphone 5 with the latest version of iOS 7. I have not changed any settings on it, I've been using it like I always have, yet one day it just started draining battery extremely fast, and now it is losing battery AS I'm charging it.

Either the battery is shot or your charger doesn't carry enough amps to charge the phone I suggest a 3.0 amp or better cord

This category is for wheeled vehicles. Try posting in the Consumer Electronics category for more answers.

I have a flip phone that lasts for a week on a change.