Battery dropping from 100% to 1% and turns off

Hello!

I bought a iPhone 6S from eBay.

I charged up the phone and replaced the battery because i tought i have some problem with the battery.

So the symptoms:

I charged up the phone with the new battery, and keeps restarting.

When i unplug the charger and trying to turn on, it’s shows the battery sign only, so I have to “charge” the phone.

When the phone is on the charger, it’s show 100% for a second, and drops down to 1% and turns off.

This is have to be one of the IC? Or something else?

Maybe the screen, or the battery is the issue?

I had the same or similar issue with the old battery.

The old battery is a replacement one with 2200mAh capacity, I got the phone like this.

It’s been restored to factory setting via iTunes and updated to the latest IOS.

Thanks!