So your iPhone won't charge past 80% even if you leave it plugged in for a long time? Don't worry, you're not the only iPhone user experiencing this hiccup and it isn't a battery issue (best check your Battery Health in Settings to be sure). All you need to do is to tweak your iPhone's Settings to make sure your device hits full battery every time you charge it.
First, let's understand why this happens. Apple first introduced a feature called Optimized Charging in iOS 13 to protect your iPhone's battery from over-stressing. The tech giant has said in the past that leaving your iPhone plugged in when it's already full for a long period of time can affect your battery health.
Your device might also stop charging when it gets too warm when plugged in, according to Apple. A fix for this is to move your iPhone and charger to a cooler location.
How to turn off Optimized Charging
How Optimized Charging works is it uses machine learning to understand your daily charging routine with your iPhone. Then, it will wait until you need to use your iPhone to finish charging to 100%, which you'll get a notification for.
To disable this feature, open Settings > Battery > Battery Health then toggle Optimized Battery Charging.
You'll then see a prompt asking for how long you want to turn it off. Choose whichever you prefer.