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)