Battery doesn’t hold the charge for long

Thank you already if you’re reading this

So I’m facing another problem with my iPhone 6s

After iOS update my battery won’t last more than 2 hours stand by or on screen use

I have already changed 2 batteries in 10 days thinking of the first battery was defective but i guess not

I have friends whose 6s working fine after the update but not sure what’s wrong with my iPhone 6s

I took my phone to nearest technician, he said that he will have to look into the logic board for some IC or something

Not sure what to do,

I have even tried restoring using all possible method ( DFU & iTunes restore )

The doubt I’m having is wether the problem is with the lastes iOS firmware or there’s something wrong with the logic board

One more thing if that helps

My phone is charging faster than usual and drains accordingly

Battery cycle is good, charges percentage by percentage no jump at all

Battery wear level is at 0% ( battery life app )

Pls help