I'm on my fourth 6S+. The first had a faulty home button and the middle two had terrible screen issues. There is definitely less battery life with a Samsung A9. My first two were TSMC and I consistently got 11.5-12.5 hours of use per charge cycle. The last two have had Samsung chips and I consistently get 9.5-10.5 hours of use per charge cycle. Same carrier, same home/work location and same usage pattern. I lose a whole *two hours* with the Samsung chip phones and that is absolutely nothing to sniff at!
I'm incredibly disappointed with the Samsung A9 battery life and with no way to tell which chip you're getting if you swap phones, it could be a long play at the exchange game. I'm really not sure that I can be bothered with all the hassle and who's to say that if I did land on a TSMC chip again that it wouldn't have a screen issue.
I buy my phones outright SIM-free and I'm not comfortable laying out so much money when I know there are 6S+ phones out there getting an extra two hours of battery life (*based on my own typical usage pattern).