Garmin devices are shipped with a USB charging cable only. This means that a charging plug has to be purchased separately. 

If an underpowered charging plug is used, it will take significantly longer to charge a Garmin device. According to specification from Garmin, a charging plug with 5V is ideal as that is the maximum a device can consume. 

Charging of a Garmin device is an hour in most cases, two at the most.