You can place Stryd on the charger. If the light comes on, Stryd is charging. Charging will complete in an hour or so. If the light stays off, Stryd is fully charged and you are ready to run.
You can also use the Stryd app on your phone to check the level of the battery.
For iOS, go to Settings and look at the battery level icon.
For Android, you need to start a run. Select Start Training and activate your Stryd by shaking it vigorously. Once the phone detect your Stryd, you will see the battery gauge top right:
Contact firstname.lastname@example.org if you experience any problems charging your Stryd.