This is a great article for you, If your iPhone 6S is one of those that’s having power issues, don’t be afraid: Apple is offering battery replacements for the faulty devices and if you are yet to have issues with your iPhone 6S battery, this particle will help you find out if you should be worried or not. The unexpected system shut-downs make it abundantly clear that something’s not quite right, but when Apple addressed the issue and announced the global replacement program, it didn’t provide an easy way to find out if your phone is affected.
Firstly check you IPhone 6S battery serial number…
HOW TO CHECK YOUR IPHONE 6S BATTERY’S SERIAL NUMBER
How to Locate your serial number;
Look at the back of your phone (below the “S” icon) or go to Settings >> General >> About (Apple gives a more in-depth guide here). Once you have located it, check if the codes in the fourth and fifth position match any of these Q/number combinations:
Q3, Q4, Q5, Q6, Q7, Q8, Q9, QC, QD, QF, QG, QH, QJ
Now, If you have a match then you should consider taking your phone in for replacement even if you haven’t had any issues. Just be wary if your screen is in rough shape — Apple says any cracks or damage will need to be fixed before a battery replacement.