Have you guys thought of using your smart phones? The nav companys are eventually going out of business because the phones are so good. With mine you have the option of paying for the service(NAV) or using Google. The Google gives you turn by turn directions just like Garvin and the others. You don't have to plug it in unsless your battery is low, then you will need a plug. The screen generally stays lit if you just have to see the map but the voice is very clear and easily heard. each address is kept in memory so it can be recalled. I haven't picked my TOM TOM up since getting my phone.
On a safety issue. We had a lot of break ins, in our neighborhood, mostly juveniles looking for whatever they could find. You would be surprised at how many people leave their laptops, cell phones cameras etc. in their cars overnight just because they don't want to carry them inside. If you have a GPS device in your car and you leave it attached to the windscreen, it is an open invitation to theives wjile at work or vacation. The worst part is that almost everybody has a saved address that will get them home from wherever they are, be it vacation or a road trip. This gives the thief your address and a road map to your home. VERY bad idea.
Suggestion:
If you have this setup, I would suggest as I did to my neighbors, to change the address to your home to some place near your home such as a landmark or even just your town, This way they won't have your address.
While I am on this theme. How many of you guys have the safety rope on your garage door that you pull when the power goes off so you can lift your door and get the car out. The little red one on most doors. this is another invitation for the thieves. They can slide a piece of 2x4 or similar between the upper section of the garage door and the frame. Then they usea piece of wire with a hook on the end to slip through and catch the rope. One tug and they are in your garage without making a sound.
Suggestion:
1. Add a motion dectector in your garage if you want to keep the rope for your wife while you are away or at work.
2. Remove the rope and make your own piece of wire(or metal rod) to slip into the release lever, and let all in the family know where it is kept in the garage.
Bill