Had one of those USB plugs when I had a Garmin 1300 and the data cable that came with the GPS would not charge or power the GPS when it was turned on. Discoverd this the 1st day out on a week trip. Would have to turn it off so it would charge then use sparingly at times. Then charge at night.

Solved the problem by getting the RoadTech 660 and fairing mount.

 

That is because there is a difference between a data cable and a power cable.
Not sure exactly what it is, but those data cables that come with the units will not power it up.

See my link above for a "power cable" option.

 

I didn't know that at the time and it was a PITA to have the thing die while on the road. I didn't know there was a cable difference.

 

I'll have to try the usb on my bike, when i hook it up to my computer it ask if i want to hook up to the computer or not. So maybe the Tomtom will charge with the usb?? Worth a shot.
Steve in Ct