You'd have t research to find out the current draw.
And a car typically doesn't have a 5v power lead.
Perhaps they're talking about a car power adapter that's specific to your NavMan unit?
Just bought a Navman 4400 BT GPS receiver but it is running on 3 ordinary AAA batteries. The manual says it can also run off a car power lead of 5V. Anyone know where I can get hold of one of these and also what milli-amp power does it use?