If your iPhone feels slow or dies fast, you may need a new battery — here's how to check

Key Points
  • It may be time for a new battery if your iPhone feels like it runs a bit slower than it used to, or if you notice that the battery life doesn't seem to be as good as when you bought it.
  • Apple software may notice that your battery is getting old and, if your phone shuts off unexpectedly, will slow your phone down in an effort to prevent it from turning off and preserve battery life.
  • Here's how to see if it's time for a new battery.
iPhone SE
Todd Haselton | CNBC

If your iPhone feels like it runs a bit slower than it used to, or if you notice that the battery life doesn't seem to be as good as when you bought it, it may be time to replace it.

That's because the batteries in the gadgets we use get slowly worse as they age. Apple's iPhone software tries to compensate for this: If your phone shuts off unexpectedly, it can will slow your phone down to preserve battery life and try to prevent unexpected shutdowns, which are an annoying surprise for most people.

But a better solution is to replace the battery entirely.

There's a way to quickly check if your phone is slowing itself down, which means you should probably send it in (or take it to an Apple Store if one around you is open) to get a new battery. 

Here's what to do.

How to check your iPhone battery health

Checking the health of my iPhone battery using iOS 11.3
Todd Haselton | CNBC
  • Open Settings on your iPhone.
  • Choose Battery.
  • Tap "Battery Health'"

Now you'll see the "Maximum Capacity." The lower it is, the less battery life you'll get. Apple's battery site says a "normal battery is designed to retain up to 80% of its original capacity" and that a one-year warranty includes service if your battery is defective.

But a one-year old iPhone should generally be fine.

My iPhone 11 Pro Max bought in September (not quite a year ago) has a 96% maximum capacity right now. You may want a replacement if you see your peak performance capacity around 80% or lower, though.

Next, check the next area down the page. If it says "Peak Performance Capability," that means your iPhone is running at full speed and you're probably OK.

But if it says "Performance management applied," that means your iPhone experienced at least one unexpected shut-down due to battery life, and Apple's software is now throttling performance to prevent that from happening again.

You can turn this off to get your iPhone running at peak speed by tapping "disable" at the end of the warning message, but the best option is to replace your battery instead.

You may also want to replace your battery if it says "Performance management turned off,"  "Battery health unknown" or "Battery health degraded." 

How to replace your battery

You might see this option if your battery is aging.
Todd Haselton | CNBC

You can replace your battery by either making an appointment at an Apple Store or by sending it in for Apple — just visit Apple's website to see what works best for you.

The good news is, a battery costs lot less than a new phone. If you have AppleCare+, which you buy when your phone is new, it's free to replace the battery.

If not, it's $69 to replace the battery on an iPhone 11, iPhone 11 Pro/iPhone 11 Pro Max, and iPhone X/XS models. Or it's $49 for the iPhone SE, iPhone SE 2, iPhone 6/6s/7/8 and their larger "Plus" counterparts.

How to keep your iPhone battery running longer
How to keep your iPhone battery running longer