Fast forward to december 2016 and Apple had a recall program for my model 6s. Great! (see ifixit for a great overview of all the battery issues). And I started 2017 with a fresh battery and all was great.
Until 2019 and the shutdowns, the unreliability and the frustration started again. The new battery health tool indicated 82%. this was not what I was experiencing phone life was not down from 15h to 12h a day it was a matter of hours. I would open up my phone only to see up to 20% of the battery capacity be blasted off in one moment. I would charge the phone up to 3 times a day. Needless to say I replaced my battery again. So let's see what happens, I should be good till 2021.
Summary2015-10: new iPhone 6s
2017-01: 1st battery replacement
2019-04: 2nd battery replacement (82% lifespan)