Here's how to tell if your iPhone needs a new battery

If your iPhone is older than about 18 months, then there's a chance that the battery is already worn.
Written by Adrian Kingsley-Hughes, Senior Contributing Editor

Is your iPhone running slow? Does it randomly crash for what seems like no reason? Does battery life drop from 100 percent charge to flat over the course of a few hours?

The problem could be a worn battery.

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In December of 2017, an age-old internet conspiracy theory that Apple deliberately slows down older devices was proved true when it came to light that Apple had tweaked iOS to quietly throttle the performance of older iPhones if the battery is showing signs of wear.

Problem is, most people are blissfully unaware of how worn their battery is.

According to Apple, the iPhone's battery is designed to retain up to 80 percent of its original capacity at 500 complete charge cycles, so if the full charge capacity is less than 80 percent of the design capacity, of the recharge cycles exceed 500, then your battery is considered worn. Problem is, Apple hasn't made any of this information available to the end user. Unless you've been meticulous about keeping battery recharge records -- and who has time for that? -- then you've probably no clue how many times you've recharged your iPhone.

Read also: Why is it taking Apple so long to update the Mac Pro?

If you are running iOS 11.3 or later, then it's quite easy to find out how your battery is coping with the demands being placed on it. Open up the Settings app and click on Battery, and then find Battery Health (Beta).

Note that this feature applies only to the iPhone 6, iPhone 6 Plus, iPhone 6s, iPhone 6s Plus, iPhone SE, iPhone 7, and iPhone 7 Plus.

If you see this, your battery is OK and you're good to go:

What you'll see if your battery is OK

What you'll see if your battery is OK

If your battery is worn out and in need of replacing, this is what you'll see:

What you'll see if your battery is worn

What you'll see if your battery is worn

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If the battery is worn you will be offered the ability to disable performance throttling, as well as get information on how to get the battery replaced. Note that if the iPhone experiences an unexpected shutdown as a result of battery performance, power management will be turned back on.

Another way to tell if your battery is worn is if your iPhone restarts and you see a notification when it reboots that says This iPhone has experienced an unexpected shutdown. Following a crash like this iOS will automatically enable performance throttling.

Are there any side effects to disabling performance throttling? Other than increasing the risk that your device will shutdown unexpectedly, no. In fact, if your iPhone has only crashed the once, disabling performance throttling might buy you extra days, weeks, or possibly months.

Or it might crash within moments!

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And it's important to bear in mind that even newer iPhones can suffer from a worn battery. Here's my experience of getting the battery replaced in an iPhone 6s that started suffering problems problems after about 18 months of use.

If your iPhone has crashed, and you do decide to turn off performance throttling, here are some tips to help minimize future crashing:

  • Try not to expose your iPhone to extremes of heat or cold, since both put a lot of stress on your battery, making it much more likely to shut down unexpectedly
  • Turning down the screen brightness seems to help, because the display is a big battery hog, and turning it down frees up some additional power
  • Some apps might be more power-hungry than others and more likely to cause crashing, so you might need to avoid using them until you get your battery replaced

If you want more information on your iPhone's battery, then you need to turn to a third-party tool called called coconut Battery (unfortunately you'll also need access to a Mac because there's no Windows/Linux version of the software available).

After you've downloaded and installed the software, you can take advantage of the 14-day free trial to test your iPhone's battery. With your iPhone connected to the Mac running coconut Battery, you get access to metrics about your iPhone that can help you determine if it's worth spending money on a new battery.

Here's a report from my aging iPhone 6 Plus:

Coconut Battery used to display diagnostic information on the battery powering my aging iPhone 6 Plus

Coconut Battery used to display diagnostic information on the battery powering my aging iPhone 6 Plus

There are three metrics worth looking at:

  • Design capacity: This is the capacity of the battery when new
  • Full charge capacity: This is the current capacity of the battery
  • Cycle count: This is how many recharge cycles the battery has undergone

In my example, the full charge capacity is well above 80 percent of the design capacity, but I have three hundred additional recharge cycles, which means the battery is running on borrowed time (and will probably give me problems in the near future). However, the only benefit I'd get from a battery replacement right now is increased lifespan as the device isn't being throttled by iOS.

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