The 9-year-old was in class at his elementary school in Deerfield Beach, Florida when it happened.
"What he told Broward Sheriff Fire Rescue was that his cellphone was beeping and making noise, so he took the battery out. When he took the battery out he apparently dropped the battery on the floor, so when he went to pick the battery up he noticed a hole in it," said Mike Jachles, Broward Sheriff's Office Fire Rescue PIO.
The third-grader then put the battery in his pants' pocket.
"About a minute later, he said that battery caught on fire," Jachles told WSVN. "He took the battery out of his pants' pocket, dropped it on the floor. It actually melted the linoleum in the floor area. It was pretty hot."
Officials evacuated the school as a precaution for about 20 minutes, until Broward Sheriff's Fire Rescue issued an all clear, at around 11:08 a.m. No one else in the school was injured.
The incident involved a Coolpad, an Android smartphone. Officials said the battery could have shorted out when it fell to the ground. Officials are trying to determine the exact cause of the explosion.