How iOS 18 will impact your iPhone's battery health – and what you can do about it

If there’s one thing that smartphone users worry about more than anything — even having an internet connection — it’s the battery. 

It used to be battery life that was the source of anxiety, with owners watching each percentage point drop with furrowed brows and dread in their hearts. As a result, the internet became awash with hints, tips, tricks, and even voodoo magic on how to improve battery life.

Also: I improved my iPhone’s battery life by changing these 10 settings

Quick tip: Want to improve your iPhone’s battery life the easy way? Put it into low power mode (tap on Settings > Battery and toggle “Low Power Mode”) and turn down your screen brightness.

Then Apple did something to change this: it gave iPhone users another number to be worried about — battery health, in the form of a “Maximum Capacity” metric. You can find this number by tapping on Settings > Battery, and then going to Battery Health.

Maximum Capacity is not a measure of overall battery wear but instead a measure of battery capacity relative to when it was new. Put another way, it’s how much power the battery can hold. The lower the capacity, the less usage you’re going to get between charges and the less peak power the battery can put out. When that number drops below 80%, it’s time to think about getting the battery or the phone replaced.

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Predictably, battery life worries have been replaced by battery health worries, and there’s no time that battery health becomes a bigger worry than when moving to a new iOS version. It’s common for social media to be flooded with stories from users saying how their Maximum Capacity score dropped precipitously following the update. And iOS 18 will be the same.

So, what’s going on here?

It’s simple — it’s normal battery wear. Every time you charge and discharge a lithium-ion battery, it experiences a small amount of wear. 

According to Apple, for the iPhone 14 and earlier, the batteries are “designed to retain 80 percent of their original capacity at 500 complete charge cycles under ideal conditions,” while for the iPhone 15, that 500 charge cycles is increased to 1,000. This means that for the iPhone 14 and earlier, every 25 charge cycles or so, the Maximum Capacity figure should drop a percentage point. For iPhone 15, it takes 50 recharge cycles for the same percentage point drop.

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But things are not as straightforward as that.

Take, for example, my iPhone 15 Pro Max. It has 117 charge cycles on it and the battery is still at 100%? Shouldn’t it be at about 98%?

iPhones can seemingly be stuck at 100% for months at the beginning of their life, and this is part of the problem as it sets an expectation that the battery isn’t wearing. The reason for this is that the battery inside your iPhone has a higher actual capacity than Apple puts in the spec sheet. 

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Apple underpromises on the capacity because new batteries have a natural variation in capacity, and Apple would prefer that your battery has more capacity, not less, than what’s in the spec sheet. This natural variation in capacity also varies, so the amount of time it takes for the battery to start ticking down also varies. 

But once the actual capacity wears down to the capacity that Apple states in the spec sheet, battery health starts to tick down.

Why do some people experience a big drop in Maximum Capacity following an update?

There are likely a couple of things at play, from people not noticing what the battery was at before the update to the update performing recalibrations to improve the accuracy of the information.

Battery wear happens.

Updates don’t wear your battery. What does is the normal charging and discharging of the battery as part of using the iPhone, along with things like subjecting the phone to overheating, and using poor quality chargers and cables.

Also: You can download iOS 18 public beta on iPhone right now. Here’s how

Battery wear is a fact of life, and despite the endless stream of blog posts and YouTube videos, you can’t keep your battery’s health at 100% no matter what you do, even if you keep it in its box in a drawer.

Eventually, that battery is going to wear.

So, keep the phone cool, use a quality charger and cable (or wireless), and get on with your life.