What the notice says
If your iPhone uses iOS 10.2.1 through iOS 11.2.6, this notice might appear in Settings > Battery: "Your iPhone battery may need to be serviced."
Why the notice appears
Using diagnostics in iOS, we've detected that the battery in your iPhone may need to be replaced. When a battery gets closer to the end of its lifespan, the amount of charge and the ability to provide power reduces. As a result, a battery may need to be charged more and more frequently and your iPhone might experience unexpected shutdowns.
This isn’t a safety issue, it’s just to let you know that your battery may need to be replaced. You can continue to use your iPhone until you have your battery checked. In the meantime, you might notice longer app launch times, lower frame rates while scrolling, and other reductions in performance. For more information on iPhone battery performance, see iPhone Battery and Performance.
All rechargeable batteries are consumables and have a limited lifespan, eventually needing to be serviced or recycled. There are various factors that can affect the performance and lifespan of your device’s battery, including number of charge cycles, chemical aging of your battery, and exposure to extreme heat or cold. Learn more about maximizing battery life and lifespan.
Get further assistance
To get help with a battery replacement, contact Apple Support for service options.
Apple’s one-year warranty, AppleCare+, and consumer law include service coverage for a defective battery. If your battery doesn't have service coverage, Apple offers a battery replacement service for a fee.
* Some counterfeit and third-party batteries may not be designed properly and could result in safety issues. To ensure you receive a genuine Apple battery, we recommend visiting an Apple Store or Apple Authorized Service Provider.