In order to properly charge trackers, please make sure that they are seated in the port with the rounded edge toward the USB and the indicator lights facing upward (as pictured below). If you had them in backward, no worries, it happens! We also recommend charging your trackers directly in the wall using a charging block, that will ensure both trackers are getting an equal amount of charge.
In the event, that your trackers are still not charging after following both steps above and/ or resemble the picture below, please email email@example.com with a picture of your trackers charging! This will give us more insight into further troubleshooting.