On a day spent near a charger, you may not need a full battery. On a long train journey, that extra reserve can matter. A useful charging setting should fit those two days differently; 80 percent is not a target you must hit at all costs.
A limit and a delay do different jobs
A charge limit tells a supported iPhone to stop near a chosen percentage. Optimized Battery Charging instead learns your routine and may postpone charging past 80 percent, aiming to finish before you unplug. A pause at 80 percent therefore does not necessarily mean a fixed limit is enabled.
Apple’s current instructions offer limits from 80 to 100 percent in five-point steps on iPhone 15 and later. Look under Settings, Battery, Charging. With the limit at 100 percent, optimized charging is available. On iPhone 14 and earlier, Apple describes optimized charging under Battery Health & Charging rather than the same adjustable limit. Check your model and installed software if the menus differ.
Choose using an ordinary day
Try a limit on a day when charging is easy. Note the battery level when you normally finish using the phone. If you regularly reach an uncomfortable level before getting home, choose a higher limit rather than reorganising the whole day around the setting.
Before an unusually long day away, review the setting in advance. Distinguish a limit you chose from an optimized-charging delay; changing the wrong one may not give you the charge you expected. Return to your usual preference afterwards if it still suits you.
An occasional full charge can be normal
Apple says an iPhone with a limit below 100 percent sometimes charges fully to keep its charge estimates accurate. That alone does not show that the setting failed.
These features aim to reduce battery wear. They do not promise a particular number of extra months, and a charge limit cannot restore capacity already lost. The practical check is whether the setting leaves enough usable charge for your day without needless time spent fully charged.