In under 18 months, my iPhone’s battery life has gone from great to terrible

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ZDNET’s key takeaways

• My iPhone is less than 18 months old.
• It now cannot make it through a day without a recharge.
• Nothing appears abnormal in the settings.

Rather than do my usual and upgrade my iPhone again last year with only about a year on the clock, I decided to try what most people end up having to do — keep it going for a few years. 

Apple says that the battery is designed to retain 80% of its original capacity at 1,000 recharge cycles “under ideal conditions.” At that point, when the battery’s maximum capacity dips below the 80% mark, it is functionally at the end of its life and will need replacing.

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So, I should be good for at least a couple of years, right? Wrong.

Some background

The battery in my iPhone 15 Pro Max was manufactured in December 2023 and first used in March 2024 (it was delivered to me on March 9). At the time of writing, it’s early September 2025, so the iPhone is around 17 months old.

Also: Changing these iOS 18 settings significantly improved my iPhone’s battery life

According to the data stored by the operating system, battery health is normal, maximum capacity is 89% compared to when it was new, and it has been through 501 recharge cycles — almost exactly halfway through those 1,000 recharge cycles.

On top of that, I have taken every possible measure to care for the battery: I have permanently set the charging limit to 80% (Settings > Battery > Charging), avoided keeping the handset on charge for excessively long periods, and ensured it remains away from extreme temperatures.

Now it doesn’t last a day

I start the day with an 80% charge because that’s the charge limit I have it set at, and by late afternoon, it’s hovering close to — if not past — the 20% zone.

This iPhone is running a beta version of iOS 26, with Adaptive Power enabled, so in theory it should manage battery consumption better. However, bugs are to be expected in beta software, so I thought that might have something to do with the issue and rolled back to the latest iOS 18 release.

Also: If these iPhone 17 Air rumors are real, my old phone is about to be retired

No. Battery life is no worse under iOS 26 than iOS 18.

Now, I am quite a heavy iPhone user. It’s never more than an arm’s reach away, and I routinely have music, Audible, or YouTube playing in the background with the screen off (yes, I’m the guy paying for YouTube Premium). That’s always been my usage pattern, so nothing has changed. I used to be able to make it to the evening. Now, early afternoon is tough.

So, what’s going on?

What I’m seeing here is a symptom of heavy usage. Not only does it use more battery during the day, but it also accelerates and intensifies battery degradation, thereby reducing the overall lifespan of the battery.

Also: The best power banks you can buy in 2025

Now, it could be just me, but a quick search suggests I’m not alone.

So, what are my options if I wanted this handset to last me three years?

Well, I’ll tell you now, I’m absolutely convinced that this handset won’t make it to the three-year mark without being a total nuisance to use. I can eke more battery life by increasing the charging limit from 80%, but that would likely accelerate battery wear.

Also: Finally, a lightweight power bank for my iPhone that can also take a beating

I could also get the battery replaced. This is what I’ll do. I’m planning on replacing this handset this year, but I can’t pass it on in this condition.

In the interim, I’ll grab one of my thin-and-light MagSafe power banks and make that part of my must-have everyday carry.