There's something wrong, but the bug is not a safety issue.
If you’ve noticed your iPhone 6S shuts down well before the battery runs out, you might be in luck. Apple announced late on Nov. 20 it would be offering replacement batteries for certain phones.
The company said in a release there’s an issue with “a very small number” of 6S models, which causes some phones to switch off before they’re out of power. Apple noted the bug is not a safety issue.
If you have an iPhone 6S built between September and October 2015, head to an Apple Store or an authorized Apple service store to see if your phone is eligible for a free battery replacement. Even if you already paid to have the battery replaced yourself, you may still be entitled to a refund.
Apple seems to have waited a healthy amount of time after the September release of its latest smartphone, the iPhone 7, to announce the replacement program. So if you upgraded because your old iPhone’s battery life was causing you grief, this might not be the most welcome news.