Has your iPhone 6s started to shut down suddenly for no good reason?
If it was manufactured sometime between September and October 2015, you might be eligible for free repairs.
Only selected units
According to the statement on its website, Apple has found that certain iPhone 6s devices will shut down without warning. Assuring customers that it was "not a safety issue" (good to know), the company stressed that the devices affected were very few and only with a "limited serial number range" manufactured during the duration between September and October 2015.
If you bought your iPhone sometime after October 2015, then there is a small chance your phone could be affected especially if it shows signs of faultiness e.g. the unexpected shutdowns.
All you need to do is visit the nearest Apple Authorised Service Provider where the iPhone will be examined and its serial number checked to see if your device did indeed fall under the bad batch.
If your phone is unfortunately one of the devices affected, then all you would need to do is hand it in and the phone's battery will be replaced. While Apple does not explicitly state the battery is to blame for the problem, Apple stating that affected devices will have their batteries replaced is a big hint.
Should your device already have some form of noticeable damage, you might be told it will need to be resolved first and in some cases (your warranty ran out) charges might be incurred. If you paid to replace your battery before the announcement and your iPhone is eligible for the free fix, you can try and contact Apple for a refun.
Do note the fix will not extend the iPhone's warranty but it will cover affected iPhone 6s batteries for three years after each unit's first retail sale.