iOS 18 introduces a warning message that appears if you use a slow charger, and updates the Battery Health chart to reflect periods of slow charging
https://www.techradar.com/phones/iphone/ios-18-will-warn-you-if-your-iphone-charger-is-too-slow
https://www.techradar.com/phones/iphone/ios-18-will-warn-you-if-your-iphone-charger-is-too-slow