Why does my FPS drops from 150 to 50?

Whenever I play games and or do editing, my FPS drops from 150 -160 to 30 - 60 and doesn't comeback for almost 3mins. Its like being unplugged from the charger even though there's no notification and is still charging. I also noticed that the it tends to get hotter than usual. I also timed how fast the battery goes, and it only lasts 30mins..

Is it an airflow issue or is it the battery?