Every smartphone battery is designed to handle a specific number of full charge cycles before its capacity starts declining.

How to fix Slow Charger battery warning To stop your iPhone being in the Slow Charger state, simply use a USB-C cable (or Lightning cable for iPhone 14 and earlier) and appropriate power brick.

When your iPhone is charging from a low battery percentage, the Lock Screen displays how long it will take to reach at least 80% charge.