Have you followed these guidelines from Apple?
If Optimized Battery Charging doesn’t activate
Optimized charging is designed to engage only in locations where you spend the most time, such as your home and place of work. The feature doesn’t engage when your usage habits are more variable, such as when you travel. Because of this, some location settings must be enabled for Optimized Battery Charging to activate. None of the location information used for this feature is sent to Apple.
Follow these steps:
- Go to Settings > Privacy & Security > Location Services and turn on Location Services.
- Go to Settings > Privacy & Security > Location Services > System Services and turn on System Customization.
- Go to Settings > Privacy & Security > Location Services > System Services > Significant Locations and turn on Significant Locations.
Note: Optimized Battery Charging needs at least 14 days to learn your charging habits, so it won’t engage before then. Also, your iPhone needs to experience at least 9 charges of 5 hours or more in a given location for Optimized Battery Charging to engage.
You may need to turn on Significant Locations to get what you’re looking for and wait the specified 14 days and charging ‘sessions’.