wonder if anyone makes a Garmin 550 cradle to usb power lead

Yes tried that, makes no difference

Hi all
Don't know if anyone can help me with this problem.
When i plug my 550 into the usb charging port on my motorcycle it goes straight into pc download mode when all i want to do is power the unit
while riding .
Does anyone know if theres a way round this without having to hardwire the nav ...