The Spytec GPS platform will display the battery percentage of your GL300 tracker in the tracker tile, giving you an indication as to when it needs a recharge.
To recharge the unit, simply take it inside and plug it into wall power. The red PWR LED will flash while the battery is charging, then will stay solid once fully charged.
Now, while the tracker has been charging, it has in all likelihood not updated its location or status to the platform and when you initially power the unit on and check the status, the same low battery percentage will remain. This will continue until the tracker reconnects to the platform and reports that it has been charged and is now at 100%.
You can take the device for a short walk to reestablish the connection. Alternatively, you can place the device near a window while charging and it may update on its usual standby schedule and report the battery level while charging.