If you're having trouble getting iMessage to work after upgrading to iOS 26, Apple is aware of the issue and has shared a fix on its support site.

Phone users are reporting faster battery drain after updating to iOS 26. Many devices lose power within hours, even with moderate use. Apple says this is largely due to temporary system activities ...

You're not the only one seeing a 'Slow Charger' message pop up after installing the iOS 26 update, but there's an easy fix.