Was it charging at the time?
The chargers Samsung provides give a very fast charge, but they also cause the battery to get quite hot. They call it “adaptive fast charging”, and the device will put out either 9 volts or 5 volts, depending on what it decides to do.
You’re probably better off to charge from a normal 5 volt USP source, like a desktop computer, or a 5 volt only charger. You get no excessive heating that way.
Ack! USP = USB /facepalm
9 volts, seriously? It’s my understanding that LiIon cells get damaged when charged above 4.2 volts.