iPhone 6 battery getting hot during charging

I've been using an iPhone 5S lightning USB cable to charge an 5, 5S, and a 6 connected to a computer.

I noticed that the iPhone 6s' battery got extremely hot during charge.

Then, when the 6 was connected I noticed that it actually was draining the battery.

That same cable would charge the 6 normally when plugged into a wall socket.

I switched the cable to the new one that came with the iPhone 6 and it works normal when plugged into a computer. No heat and it charges.

Not sure if there is a difference in the new cables or not, but I did get caught out and had to use a 30 pin with a lightning connector. It sat plugged in overnight in a wall socket and did nothing.