restart when gaming and open big app like antutu etc

ar u sure that because my battery not my iOS ? i watch my battery condition in setinggs thats still normal condition ?

there's a good chance its the battery. apple themselves are replacing batteries right now for $29 because they have acknowledged it as an issue. also the 6s is one of the best designed phones in my opinion. they rarely have board level issues besides vcc main shorts and backlight issues usually due to not disconnecting the battery before screen replacement.

Check your battery cycles via 3Utools which you can download and run on a windows computer or CoconutBattery which is an app run on Mac computers.

If the battery cycle exceeds 500 it definitely is overdue for a battery replacement.

Your symptoms definitely point to a worn battery. Even the OS is probably warning you about the shutdown issue if your phone is up to date.

guys please my new update about battery health from 3Utools

it seems like u replaced the battery recently if theres only 3 cycles on it. if you ordered it from ebay or amazon you probably got a defective battery. i know when i used to work for my old boss we used to order batteries from ebay and literally like 8/10 would be bad. i would suggest ordering one from ifixit or mobilesentrix as both of them sell high quality parts and I have never had an issue with a single battery form either vender.