why does my i phone se dies at 80 percent

You may have a defective battery, Sometimes if the phone wasn't repaired previously by someone other than apple, Maybe they will replace it for you. They always check the device history and look at the screws at the bottom of the device, If they look like someone attempted to open it they will deny service. All i can say take it to the store and see what they will tell you. Very helpful and understanding company. Best of luck :)

Don't know