This new option joins the Optimized Battery Charging setting that exists already in the Battery Health & Charging menu, found under the main Battery section of the Settings menu. This long-standing iPhone setting pauses charging at 80% during your habitual charging times and then charges the remaining 20% just before you’re likely to unplug the phone so the phone sits at fully charged (a strenuous status for a battery) for as little time as possible.
Alternatively, there’s still the option to have no charging limits at all, ensuring you get a full charge every time your iPhone’s plugged in for long enough. However doing this increases strain on the battery, likely reducing the phone’s battery health, and therefore its total maximum capacity, at a faster rate.
When the iPhone 15’s 80% charging limit was initially noticed, it was thought that it may be a previously unknown feature within iOS 17. However, it’s now been confirmed that this feature is not available on other phones running the software, which has just been fully launched. Older iPhones simply have the option to turn Optimized Battery Charging on or off, as they did previously.