What would happen if a person swallowed a battery

like a cellphone batttery

They would become a Pikachu. They would harvest the power, and electrocute any enemies in their way.

Probably choke; or the battery would make it to your stomach and you would have a stomach ache. It is unlikely that it will digest so you will have to have your stomach pumped or just make yourself throw up to get the battery out. Do us a favor and keep your cellphone out of your mouth. Lol.

This is Hypothetical... right? Depends on the size of the battery. I doubt it would be very healthy. Im sure there would be some sorta poisoning, causing shut down of the liver and other main organs.

It would be very bad. It may result in seizures death and all kinds of other awful things. If you did, you should call poison control of go to the hospital. I hope you're ok!
xoxo