Batteries are tested both on their own and while inside a device. The process focuses on how the battery behaves while charging or during calls. According to the direct of the Korea Test Lab (the other CTIA-certified battery testing lab in South Korea), batteries are also put in high temperates to simulate summer heat -- and check for the chances of overheating.

Samsung is still investigating what precisely went wrong with the Note 7. The device used batteries from multiple manufacturers, including Samsung's own SDI arm.

When the company recalled 2.5 million Note 7s with SDI batteries inside, both Samsung and Korea's Agency for Technology and Standards deemed that batteries from another supplier, ATL, didn't suffer the same issue, and replacement Note 7s with ATL batteries were offered. However, phones still went up in smoke after the first wave of recalls.

Talking to the Wall Street Journal, the CTIA's chief technology officer Tom Sawanobori said: "We've certified over 1,500 batteries. This is the first time we've had an issue."