Lithium-ion batteries chemically degrade faster if they are constantly held at a 100% maximum charge. If you plug your iPhone in every night before bed, it reaches 100% within two hours and then sits there, fully stressed, for another six hours while you sleep. Over several months, this aggressive charging cycle will permanently reduce the total capacity of your battery. To solve this, Apple engineered a machine-learning algorithm called “Optimized Battery Charging” that actively manages how your phone absorbs electricity.
How the Optimization Engine Works
When this feature is active, your iPhone uses on-device artificial intelligence to learn your daily routine. If it knows you wake up at 7:00 AM every single day, it changes how it charges overnight.
Instead of charging straight to 100%, the iPhone will rapidly charge to exactly 80% and then deliberately stop. It allows the battery to rest in a low-stress state for the majority of the night. Then, precisely at 5:30 AM (just before you wake up), it will calculate the exact amount of time needed and slowly trickle-charge the final 20%, ensuring you wake up to a 100% battery without having stressed the internal chemistry for six hours.
How to Enable the Feature
This setting is usually enabled by default on newer iPhones, but it is critical to verify its status if you plan on keeping your device for multiple years.
- Open the Settings app on your iPhone.
- Scroll down and tap on Battery.
- Tap on Battery Health & Charging.
- Look for the toggle switch labeled Optimized Battery Charging.
- Ensure the switch is turned ON (green).
If you have an iPhone 15 or newer, you will also see an additional option labeled 80% Limit. This is an even more aggressive protection mode that permanently prevents the phone from ever charging past 80%, regardless of your routine. This is highly recommended if you work at a desk all day and constantly keep your phone plugged into a charger.