Stryd can work great during ultra events that take many hours. The battery of Stryd can last up to 20 hours, and will continue to pass data to a watch or phone during that time. The Stryd platform does accept very long runs over 8 hours but there are some limitations.
1. Uploading data from Stryd with your phone (offline sync) may not work for a run longer than 8 hours.
2. GPS data of runs longer than 8 hours may not show in PowerCenter or the Stryd app on your phone.
The development team is aware of this limitation, and is considering to address this is a future release. The workaround is to analyze your data in Garmin Connect, TrainingPeaks or other platform.
If you have additional questions, contact email@example.com.