First, We have to disable the garmin_gps module, because the serial interface isn't very stable
echo "blacklist garmin_gps" >> /etc/modprobe.d/blacklist.conf
Set the correct permissions for the usb device in /etc/udev/rules.d/51-garmin.rules
ATTRS{idVendor}=="091e", ATTRS{idProduct}=="0003", MODE="0660", GROUP="plugdev"Download the stored tracks :
gpsbabel -t -i garmin -f usb: -o gpx -F file.gpx