Seems to be corrosion, was it exposed to oily or acidic air? Maybe near the kitchen?

It just shows when it stopped charging in the past and doesn’t reflect the current battery level.

https://preview.redd.it/sqxtcakkkaxb1.jpeg?width=828&format=pjpg&auto=webp&s=d3b9be644a8482b2352042516ed8db4a5ae61e53

Since always I’ve owned an iPhone

Why contacts and phone both? Contacts essentials is just less phone