Why is my iPhone 5S battery draining overnight and very quickly? A few days ago I was charging my phone in my car and it stopped charging, and I noticed that the cord had a little hole and smoke was coming out of there. I was buying some food from a local shop, and the guy working there knew me and said he had tons of cords, so he gave me one that he had at the store. After I started using this one, my battery has been going crazy. If I charge it to full power, I would wake up and find it under 10%. And if I charge it and use it during the day, it would drain very quickly. I thought the problem was because of the cord he gave me so I went to Best Buy to buy an Apple one and the guy there said that that was a long shot, and it's probably something else. I did use my uncle's iPad cord and the same problem is still there. I have no clue what happened. This battery thing literally happened overnight, it wasn't gradual and it's never been this bad. Can anyone help? 
P.S. I have iOS 8.1.2 (not the latest one due to lacking storage)
In order for cables to smoke the current must have exceeded all limits of the design by 10x.

Since the battery is connected true it, it would have gotten a shock of its life, and now no longer been able to hold the charge.

The guy at Best Buy was right, it is not the cable any more since the damage was done.