Why and how to limit iPhone 15 to 80% maximum charge


40 80 rule on iPhone
To preserve the battery in your iPhone as long as possible, follow the 40-80 rule.
Graphic: Ed Hardy/Cult of Mac

iPhone 15 has a charging trick many users might not be aware of: it can automatically stop charging when the battery level hits 80%. This makes it much easier to follow the “40-80 rule,” which helps increase the long-term useful life of the battery.

Here’s more on how it works, whether you should follow the rule, and how to flip on the setting on your iPhone.

The ’40-80 rule’ for iPhone battery charging

The lithium-ion battery in your iPhone packs a lot of power into a small space. As Apple puts it, “lithium-ion batteries weigh less, last longer and charge more efficiently.” It’s cutting-edge tech — they’re even used in most satellites. But there are limitations, of course. Nothing is perfect.

Most notably, they gradually wear out. Without going into the chemistry (you can if you want), the battery’s anode and cathode become less efficient over multiple charge/discharge cycles. And it turns out that fully charging and fully discharging a battery lithium-ion battery increases the rate at which it wears out.

Hence the “40-80 rule.” Keeping this type of battery charged between 40% and 80% gives the maximum long-term lifespan. And this isn’t only iPhone — the rule applies to Android, laptops, tablets, satellites, whatever.

Is it right for you?

Now that you know about the 40-80 rule, you have to decide if following it makes any sense for you and your iPhone.

Ignoring it won’t have any noticeable effect over the short term. I charge my iPhone 15 Plus to 100% almost every day, and drain it to under 30% regularly. The handset has already been through 82 cycles out of a potential total of about 300-500 since I bought it in 3.5 months ago, but the battery health remains at 100%.

That said, I’m not concerned about the long-term consequences on the device. I’m in the iPhone Upgrade Program and switch to a new model every year.

Those who intend to keep their iPhone for three or more years might be more interested in doing what they can to preserve its long-term battery health by following the 40-80 rule.

Just be aware this is going to be a hassle if you’re a heavy user. You’re giving up 60% of your potential daily battery capacity, and you’ll start every morning with an 80% charge.

Still, someone who frequently ends their day with the battery level over 50% and who intends to keep their iPhone for three years or more can benefit. If this is you, read on to learn how to flip on Apple’s 80% maximum battery setting.

How to limit iPhone charging to 80%

How to set 80% charging limit on iPhone
Go to the Battery section in Settings and tap on Battery Health & Charging -> Charging Optimization. Change the setting to 80% Limit.
Screenshots: Ed Hardy/Cult of Mac

To make following the 40-80 rule easier, iOS can automatically cut off charging at 80%.

But this feature is currently available only to the iPhone 15 series. If you have an earlier model, the best you can do is keep your eye on the battery level when charging.

iPhone 15 users, making the change isn’t complex but it’s so buried you’re not likely to run across it accidentally. Go to Settings -> Battery -> Battery Health & Charging -> Charging Optimization. Change the setting to 80% Limit.

You’ll get a warning about flipping off Optimized Battery Charging as Apple thinks that is the best option. And it is for most people. If you’re not most people, iPhone 15 has you covered.

Optimize Mac Charging

Your iPhone isn’t the only battery-powered Apple device that benefits from good battery management. MacBooks have built-in battery-preserving features that are supposed to optimize charging behind the scenes, but they are fairly limited. macOS learns your charging routines, and works best if you maintain that routine from day to day. But of course, that’s not always the case.

For better battery management on a MacBook, there are third-party apps that offer a lot more battery-preserving features, like Energiza Pro from Appgineers, or AlDente by AppHouseKitchen. Both of these apps offer advanced battery-management features like charge limiting, battery temperature protection, sweet-spot charging and more.

Both apps offer free 30-day trail versions, and cost about $10 for an annual subscription or $20 for a lifetime license.


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