Iphone 6s Plus and 11 and battery life- questions

I'm in the usual state of conflicting information overload and hope i can find some clarity here.

I bought a used 6s plus last week to replace a 6s, which is on 10.3.1. The Plus came with 11.1 on

it. I upgraded to the latest iOS - presently 11.2.2 - after doing a migration from my 6s backup.

Haven't activated with Sprint yet. The 6s plus has had about 2 years of normal eveyday use.

What can i expect as far as battery life vs the 10.3.1 on the 6s? Can i or should i revert

to any earlier ios 11 version for best battery peformance?

Is there any hope that newer ios 11 versions will improve battery drain issues i'm reading

about ? I learned from Apple tech about the battery replacement option which is good and will

probably do that before end-of-year, but unclear whether that will resolve any inherent ios fast battery

drain issue if it is a product of the system and phone model, vs the battery itself.

I know that on my 6s - which I kept on 10.3.1, battery seems to run down fast doing basic tasks vs.

older (iOS 9) - and hear 10.3.3 was an improvement - but alas, I cannot simply upgrade to that version

from 10.3.1…and anyway, it is too late apparently for me to bounce my iTunes 10.3.1 backup onto the

new 6s Plus I got, since it already had some version of 11 on it, right?

I believe IPSW for 11.1 is still signed, but not sure if it is worth bothering with and AFAIK there is still

no way to go back to 9 or 10. Appreciate any opinions/input.

Thanks,

Mike