Why is my iPhone now getting warm and battery fading?

Over the past couple of weeks, I have noticed my iPhone 7 feeling very warm to the touch while in use and the battery life draining quickly. Now I can't even use it while plugged into power without the power slowly draining where before it would slowly charge the device. I often use it as a GPS and where before it would stay charged (plugged into the car), now it quickly starts to lose power. I check battery usage and force quit any apps I am not using. Am I the only one? What happened?! Running the latest iOS but this was happening a few weeks before the recent upgrade.