I have the 6s and since upgrading to 14.2 (at the advice of apple support, I was on 13.6) the phone keeps shutting down completely without warning even though it was fully charged and there is a fully charged Apple OEM battery case attached. What is extremely frustrating is it would happen randomly. Plugging the phone in doesn't always bring it back to life immediately either. Battery health is over 90% as it was replaced at the end of the free replacement program. Went to the Genius Bar and the person told me I need a new phone which is b.s. in my opinion. It's a software issue that is causing the phone to shut down, giving false battery level readings sometimes, and sometimes completely draining the battery. I have paired down as many of the background updates, background apps to the bare minimum already. I'm very hesitant to upgrade to 14.3 as it doesn't look like it would solve the problem. Apple needs to own up that they have messed up again with older phones and the new iOS and get a fix out ASAP. At this point I'm even hesitant to upgrade my iPad Pro's iOS from 13.6. In these economic times I can't afford to replace this phone now. Someone at Apple needs to respond.