iPhone 80% charge limit after three years: MacRumors' Pro Max batteries held between 88 and 97 per centiPhone 80% charge limit after three years: MacRumors' Pro Max batteries held between 88 and 97 per cent

MacRumors has published three years of battery figures from iPhones kept at Apple's 80 per cent charge limit, and the newest phone, an iPhone 17 Pro Max, is at 97 per cent of its original capacity after a year.

The figures come from MacRumors writer Juli Clover's own phones, each set to the limit from the start and used as a daily phone for its first year:

After their first year both older phones had read 94 per cent. In the past year, as test devices with few cycles (17 for the 15 Pro Max, 44 for the 16 Pro Max), the 15 Pro Max lost nothing and the 16 Pro Max lost one point. Clover also charged the 17 Pro Max over USB-C more than wirelessly this year, and suggests its vapour chamber cooling may matter more than either.

How does Charge Limit work?

On iPhone 15 models and later, Settings, Battery, Charging offers a limit from 80 to 100 per cent in 5 per cent steps, Apple's support article explains. Optimized Battery Charging, which holds the phone at 80 per cent overnight and finishes before it expects to be unplugged, is only available when the limit is 100 per cent. iOS can also recommend a limit from your habits, Apple says, such as 95 per cent.

Apple's battery page gives the benchmark: iPhone 15 batteries are designed to keep 80 per cent of their capacity at 1,000 complete cycles under ideal conditions, against 500 cycles for iPhone 14 and earlier.

Is the 80 per cent limit worth it?

On these numbers, probably not for most people. Clover reaches the same conclusion for the two older phones and suspects the 97 per cent reading is not far from what phones charged to 100 per cent show. The test has no control: there is no matching phone charged to full, so it cannot separate the limit's effect from normal ageing. All three batteries are well inside Apple's own design curve, which allows a 20 per cent loss over 1,000 cycles, and none is near that many cycles.

The figure we find most telling is the year the 15 Pro Max spent with only 17 cycles and lost nothing. That suggests cycles, and the heat that comes with charging and heavy use, do most of the damage, and simply sitting at a capped charge does little. That fits Clover's own hunch about cooling.

Our take

Three phones from one owner, using one kind of charger each year, is an anecdote, not a study, and MacRumors presents it as such. Apple's battery health reading is itself an estimate that can move after a recalibration. Even so, the direction is consistent across three years, and it matches how lithium-ion cells age.

APPDOOK's advice is the one Apple's own design implies. Leave the limit at 100 per cent with Optimized Battery Charging on if you need the full battery every day. Use 90 or 95 per cent if your phone spends long hours plugged in at a desk. Reserve 80 per cent for people who never get near an empty battery anyway. Keeping the phone cool while it charges, especially on a wireless pad, probably matters more than any of those settings, and losing a fifth of every day's battery to save a few points of capacity three years later is a poor trade for most people.