Iphone 6s has been charging for 4 days straight?

How do i fix it

Added (1). and its still dead

What the hell are you waiting for? Take it to an apple store and get it fixed. Are you sure it's charging? Maybe it's the charger's fault

No

Battery maybe shot, get it repaired

Turn it off while charging.

Isk

Take it to an Apple store and if the battery does not actually charge, you get the battery replaced. If there's no longer any warranty on the phone, Apple can still do this for an out of warranty fee. Find out what it cost from Apple and the contact at least 4 cell phone repair shops near you, and decide which repair will cost you less, and go with that option.

Apple will check to make sure the battery is the issue, the repair shop will do what you tell them to do, so if you tell to to put a new battery in the phone and that does not fix the problem you still pay for the battery.