The 6s's battery was fine until iOS 11. I've been running iOS 12 for a day now, and I notice an improvement in battery over 11.
Re:iOS 12, reviewed
by mixmastamyk on Tuesday September 18, 2018 @07:51PM
(#18020411)
iOS 11 reduced my battery life significantly over iOS 10. Don't have hard numbers but it felt like ~30%.
I updated my 6s and reset it to see if that improves the battery life situation.