The idea that a worn battery slows an iPhone is true in a narrow, specific way. Apple explains it in detail, and it is less sinister than the internet makes it sound.
Why a battery can limit performance
As lithium-ion batteries chemically age, they hold less charge and their impedance rises. When a battery cannot deliver enough power at once, the phone could shut down unexpectedly. To prevent that, iOS uses performance management, which looks at temperature, state of charge and battery impedance and, only if necessary, limits the maximum performance of some components such as the CPU and GPU.
What you might notice
Apple lists effects in more extreme cases:
- Longer app launch times
- Lower frame rates while scrolling
- Backlight dimming (which you can override in Control Center)
- Lower speaker volume by up to 3 dB
- Gradual frame rate reductions in some apps
- In the most extreme cases, camera flash disabled
What it does not affect
Apple says many areas are not affected, including cellular call quality, network throughput, photo and video quality, GPS, location accuracy, sensors and Apple Pay.
When it happens
You are more likely to see it with a low state of charge, a higher chemical age or cold temperatures. For low charge and cold, Apple says changes are temporary. If the battery has chemically aged far enough, the changes might be more lasting.
How to check
Go to Settings, Battery, Battery Health. Apple says you can see whether performance management is on, and that it is enabled only after an unexpected shutdown first occurs on a device with a diminished battery. For how long batteries last, read our iPhone battery lifespan guide.
Is it a reason to replace the battery?
If your phone is slow only when the battery is low or old and you see the effects above, a new battery can restore normal behavior. If the phone is slow for other reasons, a battery will not help. That is our interpretation of Apple’s description, not a guarantee.
Frequently asked questions
Does Apple slow down old iPhones on purpose?
Apple says performance management exists to prevent unexpected shutdowns, and only acts when needed.
Can I turn it off?
Apple says you can choose to turn it off in Battery Health once it has been enabled, but doing so can lead to shutdowns.
Sources
Last checked November 3, 2026. Apple changes its instructions between updates, so if a menu looks different on your Mac, check the linked Apple page.
