What happens if a child swallows a battery?

When I was younger, I used to swallow dental floss. One day, I was going to the bathroom, and it started to hurt. When I got up, the dental floss was coming out of my butt. My parents called the doctor and they said, not to bother it. I ate a lot of soft foods and drank plenty of water. A couple hours later, it slid right out.