Does this iPhone feature actually help protect your battery? The numbers don't lie

Apple has been working on building features into iOS that claim to help slow down premature battery wear.

First, we got optimized battery charging that paused charging at 80% and only added the last bit of charge in time for you to wake up. Then there was the 80% limit that hard-capped the charge level. Now, we have a customizable hard-capped limit between 80% and 100%.

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While there’s no doubt that capping the charge capacity helps prevent battery wear on the chemical level, does this make a measurable difference in the real world?

Juli Clover, Managing Editor at MacRumors, decided to take a look at how the battery in her iPhone was holding up. Her iPhone 15 Pro Max had the 80% limit set, and there was a “70/30 split between wired charging and MagSafe charging.” According to Clover, the battery was allowed to “get quite low before charging, and it didn’t sit on the charger for long periods of time too often.” Plus, “charging was done in a room at 72 degrees” — pretty much ideal conditions.

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So, how’d the iPhone’s battery hold up?

Clover’s battery capacity is currently at 94% with 299 cycles. Clover polled a couple of other MacRumors staffers with iPhone 15 Pro Max handsets and got one with a capacity of 87% after 329 cycles, and another with a capacity of 90% after 271 cycles. 

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To throw another data point into the mix, my iPhone 15 Pro Max is at 100% capacity after 169 charge cycles. How can we make sense of this?

According to Apple, iPhone 14 models and earlier are designed to retain 80% of their original capacity at 500 complete charge cycles under ideal conditions, while the batteries in iPhone 15 models can retain 80% of their original capacity at 1,000 complete charge cycles, again under ideal conditions. 

But what are those “ideal conditions”? Probably the battery in a lab somewhere being charged using lab equipment and kept at a constant temperature.

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Coming back to those numbers, we can say that roughly every 25 cycles for the iPhone 14 or earlier represents a one percentage point drop in charge capacity, while for the iPhone 15 and 16, this doubles to 50 cycles for every percentage point drop. That Clover’s handset has had 299 cycles and only dropped 6 percentage points is almost bang on the money, while the other handsets seem to have suffered more battery wear, averaging at around double what Clover’s iPhone has seen. 

This makes me wonder if limiting the charge to 80% is part of those “ideal conditions.”

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So where does that leave mine going through 169 charge cycles but still being at 100%?

This is another spanner in the works. Not all batteries are created equal. The battery inside your iPhone actually has a higher capacity than the nominal capacity Apple puts in the spec sheet. 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, which means the amount of time it takes for the battery to start ticking does, too. iPhones can appear to be stuck at 100% for months at the beginning of their life, which sets an expectation that the battery isn’t wearing. But it is. Once the actual capacity wears down to the capacity that Apple states in the spec sheet, battery health starts to tick down.

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The bottom line? Limiting charge capacity to 80% saves on battery wear and brings battery wear closer to what Apple says is possible under ideal conditions.