In addition to existing 100, 25, and 0 battery charge percentage icons, SF Symbol 3 introduced 75 and 50 for devices running iOS 15.
- Use the additional symbols when available on iOS 15
- It's probably a good idea to discuss with the maintainers the percentages for each symbol and get a confirmation
- Try to eliminate the "unknown state" in the current codebase
- okay to use precondition to assert certain conditions are met in the catch-all branch, or fatalError for the impossible branch