Here's some news from Apple iPhone 6s owners. If your device is unexpectedly powered off even on a full charge, you can visit your nearest Apple dealer and find out whether you're eligible for a free replacement battery.
The American tech giant announced earlier this week that a certain number of devices manufactured between September and October 2015, may shut down unexpectedly due to some battery issues. A statement issued by the company states "If you have experienced this issue please visit an Apple Retail Store or an Apple Authorized Service Provider and have your device's serial number checked to confirm eligibility for a battery replacement, free of charge."
Furthermore, Apple even emphasized that it is merely a battery life issue and nothing to do with the safety of the device. The device is 100% safe.
So if you are one of those been having power issues with your phone, you can either talk to Apple support online or visit an Apple retail store to find out if your device is eligible for a free battery replacement.