Our intention for iPhone is to deliver an experience that is simple and easy to use. Doing so requires a lot of engineering and many advanced technologies. One important technology area is battery and performance. Batteries are a complex technology, and there are a number of variables that contribute to battery performance and related iPhone performance. All rechargeable batteries are consumables and have a limited lifespan—eventually their capacity and performance decline so that they need to be serviced or recycled. As this happens, it can contribute to changes in iPhone performance. We created this information for those who would like to learn more.

About lithium-ion batteries

iPhone batteries use lithium-ion technology. Compared with older generations of battery technology, lithium-ion batteries charge faster, last longer, and have a higher power density for more battery life in a lighter package. Rechargeable lithium-ion technology currently provides the best technology for your device. Learn more about lithium-ion batteries.

How to maximize battery performance

“Battery life” is the amount of time a device runs before it needs to be recharged. “Battery lifespan” is the amount of time a battery lasts until it needs to be replaced. One factor affecting battery life and lifespan is the mix of things you do with your device. No matter how you use it, there are ways to help. A battery’s lifespan is related to its “chemical age,” which is more than just the passage of time. It includes different factors, such as the number of charge cycles and how it was cared for. Follow these tips to maximize battery performance and to help extend battery lifespan. For example, keep iPhone half-charged when it’s stored for the long term. Also avoid charging or leaving iPhone in hot environments including direct sun exposure for extended periods of time.

When batteries chemically age

All rechargeable batteries are consumable components that become less effective as they chemically age.

As lithium-ion batteries chemically age, their ability to hold a charge diminishes. This may result in shorter amounts of time before a device needs to be recharged. In addition, a battery’s ability to provide power quickly may decrease. In order for a phone to function properly, the electronics must be able to draw upon instantaneous power from the battery. One attribute that affects this instantaneous power delivery is the battery’s impedance. A battery with a high impedance is unable to provide power quickly enough to the system that needs it. A battery's impedance can increase if a battery has a higher chemical age. A battery’s impedance will temporarily increase at a low state of charge and in a cold temperature environment. When coupled with a higher chemical age, the impedance increase will be more significant. These are characteristics of battery chemistry which are common to all lithium-ion batteries in the industry.

When power is pulled from a battery with a higher level of impedance, the battery’s voltage will drop to a greater degree. Electronic components require a minimum voltage to operate. This includes the device’s internal storage, power circuits, and the battery itself. The power management system determines the capability of the battery to supply this power, and manages the loads in order to maintain operations. When the operations can no longer be supported with the full capabilities of the power management system, the system will perform a shutdown to preserve these electronic components. While this shutdown is intentional from the device perspective, it may be unexpected by the user.

Preventing unexpected shutdowns

With a low battery state of charge, a higher chemical age, or colder temperatures, users are more likely to experience unexpected shutdowns. In extreme cases, shutdowns can occur more frequently, thereby rendering the device unreliable or unusable. iOS 10.2.1 (Released January 2017) includes updates for previous models of iPhone to prevent them from unexpectedly shutting down. This includes a feature for iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, and iPhone SE to dynamically manage the instantaneous performance peaks, only when needed, to prevent the device from unexpectedly shutting down. This capability was also extended to iPhone 7 and iPhone 7 Plus with iOS 11.2, and we will continue improving our power management feature in the future. This feature’s only intent is to prevent unexpected shutdowns so that the iPhone can still be used.

This power management works by looking at a combination of the device temperature, battery state of charge, and the battery’s impedance. Only if these variables require it, iOS will dynamically manage the maximum performance of some system components, such as the CPU and GPU in order to prevent unexpected shutdowns. As a result, the device workloads will self-balance, allowing a smoother distribution of system tasks, rather than larger, quick spikes of performance all at once. In some cases, a user may not notice any differences in daily device performance. The level of perceived change depends on how much power management is required for a particular device.

In cases that require more extreme forms of this power management, the user may notice effects such as:

• Longer app launch times
• Lower frame rates while scrolling
• Backlight dimming (which can be overridden in Control Center)
• Lower speaker volume by up to -3dB
• Gradual frame rate reductions in some apps
• During the most extreme cases, the camera flash will be disabled as visible in the camera UI
• Apps refreshing in background may require reloading upon launch

Many key areas are not impacted by this power management feature. Some of these include:

• Cellular call quality and networking throughput performance
• Captured photo and video quality
• GPS performance
• Location accuracy
• Sensors like gyroscope, accelerometer, barometer
• Apple Pay

Get further assistance

For a low battery state of charge and colder temperatures, power management changes are temporary. If a device battery has chemically aged far enough, power management changes may be more lasting. This is because all rechargeable batteries are consumables and have a limited lifespan, eventually needing to be serviced or recycled. If you are impacted by this and would like to improve your device performance, replacing your device battery can help.

Learn more about battery service and recycling.