Modern smartphones use lithium-ion batteries. While these batteries charge quickly and hold a lot of power, they are incredibly sensitive to stress. One of the absolute worst things you can do to a lithium-ion battery is keep it plugged in at 100% capacity for extended periods. The constant “trickle charging” required to keep the battery completely full generates heat and chemically degrades the battery cells faster than normal use.
Unfortunately, most people charge their iPhones overnight while they sleep. This means the phone hits 100% around 1:00 AM and sits there, under stress, for another six hours before the alarm goes off. Over a year, this habit can drastically reduce your battery’s maximum capacity, forcing you to replace it prematurely.
To combat this, Apple introduced a brilliant software feature called “Optimized Battery Charging.” This guide explains how to enable it and how it works to save your battery’s lifespan.
How to Enable Optimized Battery Charging
This feature was introduced in iOS 13 and is usually enabled by default on newer iPhones. However, if you restored your phone from an older backup, or accidentally toggled it off, you should verify that it is active.
- 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. Click the toggle to turn it On (green).
How the Feature Actually Works
When you enable Optimized Battery Charging, your iPhone uses on-device machine learning to study your daily routine. It pays attention to when you usually plug your phone in at night and, crucially, when you usually wake up and unplug it.
Once it learns your schedule, the charging behavior changes dramatically:
- When you plug your phone in at midnight, it will rapidly charge up to 80% as normal.
- Once it hits 80%, the iPhone physically stops accepting a charge from the cable. The battery is put into a resting state, preventing the stressful 100% trickle charge.
- The iPhone continues to monitor the time. About an hour before you normally wake up (e.g., around 6:00 AM), it allows the charger to push the battery from 80% up to 100%.
By the time your alarm goes off at 7:00 AM, you have a completely full battery, but the phone only spent a few minutes sitting at 100% capacity instead of six hours.
Important Caveats
Because this feature relies heavily on machine learning and location tracking, it requires a predictable routine to function correctly. If you work rotating shift schedules and wake up at wildly different times every day, the iPhone will never establish a baseline routine, and the feature may not activate.
Additionally, Optimized Battery Charging is designed to only engage in locations where you spend a lot of time (like your home or office). It uses location services to determine this. If you are travelling and staying in a hotel, the feature will automatically disable itself, ensuring your phone always charges straight to 100% as quickly as possible when you are on the road.