My luck I would be at 2 hours 5 min. going 85...richm said:In my other vehicles, I use a battery operated one that I purchased at Costco. I am very happy with it. I get about 40 hours of use on rechargeable AA's. To save battery life, it automatically turns off after two hours if you don't press a button. It rests on the dash and mounts with suction cups on the glass.