Firstly check you IPhone 6S battery 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. If that’s the case, you will have to be paying for some compulsory service. So what do you think about this?