With the iPhone 15 and iPhone 15 Pro, Apple added a new battery management feature where users can charge those phones to a maximum of 80 percent instead of 100. It’s also possible to view the charging cycles in the battery settings. These features have carried over the the recently released iPhone 16 lineup.
Why stop charging at 80 percent? It has to do with battery chemistry and the effects of charging over the long haul. A lower percentage results in fewer full charging cycles, which helps extend the viability of the battery. But charging to 80 percent means you effectively have less charge on your phone for your daily use. So the daily sacrifice worth the long-term effect? We wanted to find out.
Macwelt (Macworld’s sister site in Germany) held a survey on Facebook Germany, asking readers to post screenshots of their battery settings and enter their charging behavior–whether they always or almost always charge to 100 or only to 80 percent. In less than 24 hours, we received more than 100 usable responses.
To visually assess the influence of charging behavior on battery health, we have presented the responses in a combined box and Beeswarm plot.
The two colors or lines on the Y-axis represent the data points in the two categories, people who only charge their iPhones to 80 percent and those who charge them to 100 percent. The number of dots shows how many people with the respective battery capacity we counted in each category. We counted 56 users who charge their iPhones to 100 percent and 46 users who only charge to 80 percent. The two groups are not the same size, but close.
The superimposed boxes in the diagram show the cumulative analyses of the data. The box in the 80 percent category tends more towards the edge of 100 percent capacity– it appears that the users who charge their iPhones to 80 percent tend to have a healthier battery in the long term.
We tested this hypothesis using a T-test, a common statistical method to prove that two independent groups differ significantly from each other. If the P-value is less than 0.05, (less than 5 percent), the two groups differ significantly. If the P-value is higher, the factor under investigation (in our case, the charging behavior) does not influence the data collected.
We calculated the T-test once with the entire 102 data points in the table and obtained a P-value of 0.047121 (4.7121 percent). In the second calculation, we filtered out all data points where the charge cycles were less than 140, as the battery cannot be expected to age significantly up to 140 charges. Here we obtained 89 data points, six data points less in each category. But even with this data, the calculated P-value was 0.047547 (4.7547 percent). We can therefore say that charging behavior has a statistically significant influence on battery health and longevity.
Based on our data, it can be said with certainty that users who do not charge their iPhones to 100 percent are conserving the battery through this behavior. The maximum capacity of the battery decreases somewhat more slowly when charging to 80 percent than when charging to 100 percent.
For more information, you can learn about properly changing your iPhone.