ROCHESTER, Minn. (WCCO) – An eighth grader is recovering at home Thursday night with second degree burns after his cell phone battery exploded in his pocket while at first period at Kellogg Middle School in Rochester, Minn.

The boy’s mom said her son first heard a hiss, and then a pop before the smartphone slid down his leg.

The battery had burned a hole through his pocket. Teachers helped him put out the fire and his parents took him to the hospital.

At this point, no one has any idea why this happened.

Nate McGuine with Fastphonerepair.com said exploding cell phone batteries are very rare. He said they can be caused by a variety of issues, such as excessive charging, excessive heat, or batteries being old.

“What happens is the cells break down, and they expand,” McGuine said. “They don’t have anywhere to go because batteries are tightly sealed and they can actually explode out.”

McGuine said lithium ion battery fires affect all kinds of phones.

He recommends not using after-market charges, or after-market replacement batteries, and suggests getting your cell phone battery replaced every one to two years.