My iPhone 6s keeps turning off, it says I have 100% battery turns off when I turn it on it says I have 10% battery even though I haven’t used my phone???

Hi

Go to apps store download Battery life it will test your battery condition.

But I think you need a new battery Make an appointment at Apple store.

Or go to Support.apple.com for posting details.

Cheers

Brian 🇬-1F1E7;

Make an appointment at the Genius Bar or an authorized service provider to have the phone evaluated.

Third opinion here. Like the previous advice by others it’s probably the battery. If you have an Apple store near you they will diagnose it and replace the battery for around $80.