I have a 6 (for work) and a 6S (for me). Both batteries are still in good (and very good for the 6S) condition. I run pretty much stock phones; I don't install

I have a 6 (for work) and a 6S (for me). Both batteries are still in good (and very good for the 6S) condition. I run pretty much stock phones; I don't install many apps and the ones I do are generally well behaved (nothing like Facebook, Snapchat, etc). iOS 11 on the 6S was (is?) a complete sh%$show. Very unstable. Tried normal releases, betas, dev betas, DFU after DFU after DFU. Nothing helped. I finally went back to 10.3.3 and could not be happier. The 6 is running fine on ios 11. It lags when opening iMessage or email, but that's probably more due to the 1GB RAM than anything else.