This is a video of a phone battery exploding after a man in China bit into it. If you're looking for a reason why he did it, none was given beyond, "He likes to put things in his mouth." Seriously.
"I'm the person involved," she wrote. "...I haven't been disfigured; thanks for your concern. He didn't [bite the battery] because he wanted to test its authenticity; actually my partner just has the habit of putting things into his mouth and nibbling on them. I'm okay, just my bangs were burnt a little bit. My first reaction was 'Are my eyebrows okay?'"
She added that the battery her partner had bitten into wasn't a genuine iPhone battery.
Look, I like to eat phone batteries as much as the next person, but I save that kind of stuff for the privacy of my own home. Also, don't eat batteries. You'll die. Also they'll make you fat.