Just had a quick look at Garmin webshite and found this
Garmin Support
Frequently Asked Questions
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How can I tell if my automotive device is fully charged?
04/11/2014
There are three ways to charge the internal battery in your automotive GPS device.
1.Use the provided vehicle power cable that came with your GPS device. The device will charge while powered-on and using the device, as well as when the GPS device is powered off and
plugged into a running vehicle.
2.Use an AC power adapter. Some devices come with this power cable to plug the GPS device into a wall outlet allowing the GPS device to take a charge. For devices that do not come with
this cable, one can be purchased from Garmin's online store.
3.For most devices, the final way of charging the battery is to plug the GPS into a powered-on computer with a USB cable.2 This method of charging will be a trickle charge and it may take
longer than the other two options, however it will still charge the battery. A full charge via USB may take as long as 8-12 hours. A USB cable is provided with certain GPS models.
For devices that do not come with this cable, one can be purchased from Garmin's online store.
Please note: All devices will come with a suction cup mount and vehicle power cable to charge the device. However, only some models come with an AC power cable and/or a USB cable.
If either cable did not come with the device, they can be purchased from Garmin or Garmin's dealers. To purchase one from Garmin, please visit our website at
https://buy.garmin.com/shop/
Garmin only recommends using an AC power charger that is purchased from Garmin. Third-party cables may not charge the nuvi. The message "Attached power cable cannot charge device.
Please use the cable provided with your device" may display on the device if using a third-party charger or third-party USB adapter, etc.
1Please note that temperature can play an effect on the charging of a device. If the battery registers a temperature of 0°C (32°F) and below or 45°C (113°F) and above,
it will not charge. When connected to external power, it will only be operating off of external power.
2The Quest, Quest 2, and nuviCamLMTHD will not charge using a USB cable.
Will have another go at charging maybe give it a little longer via usb, my 550 didn't take very long.