I have a problem with my iPhone 6s plus battery. When it gets to less than 30% the phone will shutdown and will not restart unless I connect it to the charger. Once it restarts it shows the same battery percentage as before it shutdown.

I have an ongoing problem with my iPhone 6s plus battery. I have had "support" from Apple telling me there is nothing wrong with the battery, I've been to the store and had them test it, and I have had two replacements and they have all done the same thing, even starting the replacement up as a new phone so that there are no apps that might be contributing to the problem. I repeatedly told them it was their software problem but they said they had "never heard of anyone having this problem". I didn't update to the latest software to see if the problem still occurred and at first it didn't, but then it was back to shutting down at 30% or less even though there was adequate power to continue for much longer. I updated to the latest version because it referred to a "correction of battery problems". Unfortunately it made no difference at all. I have had iPhones for many years and have always been a fan, but my next phone will be a Samsung unless Apple admit to their problem and sort it out.