Why Apple does not give optimized battery charging feature on iOS 12.5.5

Old iPhone users from iphone 6 plus and below really need this

Because the old iphone lines from iphone 6 plus and below have very low battery capacity, the time to use normal tasks such as facebook, messenger, youtube... is only about 3-4 hours if the battery capacity is real. of iphone is 100% (no bottle)

And when the battery is more than 20% bottle, ie charging 500 cycles, the iphone performance is significantly reduced, when using the above tasks, there is a state of shock and lag.

So I hope Apple will try to release another update, iOS 12.5.6 and add this feature in that update. If so, iPhone users from iphone 6 plus like me will be very satisfied and grateful to Apple. Friendly welcome