Find out if your iPhone 6S is eligible for a free battery replacement - CNET
Amazon.co.jp: YONTEX iPhone 6S Battery Replacement, Large Capacity, 2650 mAh, 28% More Capacity, PSE Standard, Replacement Kit and Film Included, Compatible with iPhone 6S (A1633, A1688, A1700) : Electronics
I got my iPhone's battery replaced, and I'm angry Apple didn't tell me to sooner - The Verge
Here is how to find out if your iPhone 6s is eligible for a free battery replacement