To reduce battery wear, the iPhone learns from daily charging cycles so that the battery can wait until charging is completed above 80% until you need to use the device.
In other words, up to 80% of the iPhone will charge at normal speed, and then it will decrease. At the same time, the phone will be charged by the time the user needs it. The algorithms of iOS 13 will follow this.
Download iOS 13: direct download links
How to install iOS 13 now: instructions and direct links