My iPhone wont charge on any charger

So I just bought a refurbished Iphone 5s from Straight talk. The first night i had it i updated it from ios 8.4 to ios 9.1. It was fine and that first night i had the phone it charged fine. But the next day i got it activated, and used it for about an hour. I noticed it did get alittle warmer than i felt like it shouldve. When the battery got low i plugged it in and nothing, no charge. None of the chargers i tried to use would work, whether it was an apple charger or not. NOTHING WORKED!!! A relative of mine plugged it into his iphone 6 charger which was plugged into a wall usb that had multiple usb's at both 1 amp and 2.1 amps. it charged on the 2.1 amp usb. But i went home and it still wouldnt work on any of my chargers. After fiddling with it for almost two days i finally got it to charge halfway but i picked it up to check it and it stopped again and i couldnt get it to start charging again. everytime i plug it in while its turned off or dead, it turns on and as soon as it comes on it has the charging symbol by the battery but then it instantly turns off. im really puzzled and cant find answers for this. im assuming i need to replace the port and battery but dont want to do all that to find out it is a motherboard issue.