Analysis: Does wireless charging wear down your iPhone battery?

Macworld

A year ago, Macwelt (Macworld in Germany) surveyed Facebook readers about their iPhone charging behavior and found that the charging limit introduced by Apple contributed to the slowdown in battery ageing. This year, Macwelt asked about another factor in charging behavior: whether users prefer to charge their iPhones inductively or by cable, and whether this type has a significant impact on maximum capacity.

Macwelt asked about charging behaviour on the Macwelt Facebook page and asked fans to post a screenshot of their battery status, and to write whether they use the charging limit and, if so, up to what percentage of the maximum capacity. Also, we asked if the iPhone was charged inductively via MagSafe, by cable, or a mixture of the two. Up to 300 comments were collected, with around 230 usable data points. We analyzed the data using various methods.

General results

The entire data set is summarized in the diagram below, which shows the relationship between the maximum capacity of the battery and the charging cycles on two axes. Two factors of the charging behavior are shown in the color and shape of the respective data point: Possible charging limits are shown on a colored scale, while the shape reflects the charging behavior.






The data visualization shows that the maximum battery capacity lasts for quite a long time. Between 200 and 300 charging cycles must be completed before the maximum capacity drops below 99 percent. In our data set, I found an iPhone with 267 charging cycles that remained at 100 percent of its maximum capacity.

The decay of the maximum battery capacity is therefore not strictly linear, but follows a curve. Initially, the maximum capacity is maintained for several months, and it only begins to fall starting at 230 charging cycles, on average. At first glance, there are more red and light red data points at the top, which may indicate charging limits of 80, 85, and 90 percent. But let’s take a closer look at these ratios.

Charging limits and the effect on battery health

In our survey last year, we found that setting a charging limit of 80 percent can potentially slow down battery ageing. As of iOS 18, Apple has broken down the settings for charging limits more granularly: You can set the limit at 80, 85, 90, and 95 percent. This innovation is reflected in the current survey; half of the participants charge without restriction, a quarter prefer a charging limit of 80 percent, and 6 to 11 percent of those surveyed switched to three other options. Graphically, the distribution looks as follows:






The boxplots can be interpreted to mean that the charging limits have a slight effect on the maximum battery capacity. The iPhones with a charging restriction of 90 percent or lower tend to have a larger battery capacity.

I also tested this thesis numerically by carrying out a regression analysis in Excel. This can analyze whether there is a correlation between the maximum battery capacity and the charging limit, and how strongly the charging limit affects the battery capacity.

In fact, the regression analysis shows a significance quotient of 0.00045, which means that there really is a correlation between the charging limit and battery health. However, the effect is quite small; only five per cent of battery ageing can be explained by the charging limit, the rest depends on other factors.

Wireless charging

The same question now arises regarding charging behavior: Does charging via MagSafe or cable affect the longevity of the battery? And if so, how strong is this effect?






This chart shows the relationship between the charging behavior and the maximum battery capacity. The result is not so clear at first glance. I have therefore also carried out the regression analysis for the charging behaviour. The significance quotient here is 0.378, so there is no correlation between charging behavior and battery ageing.

Whether you charge your iPhone inductively, by cable, or alternately has no effect on battery longevity. However, we would recommend setting the charging limit to 90 percent or less. If you keep your iPhone for a year or more, your battery will tend to age more slowly.

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