Have never used the battery more than 15 minutes, so I can't tell you how long it will last - it should be plugged into the mount where it will receive power from.
Overall a good GPS, I'd buy another. The large screen is great and the speaker is loud so you can her the instructions over the MH noise when in heavy traffic so you don't have to watch the screen all of the time.
I use mine for both the MH and the Jeep, you just have to remember to switch it back and for the vehicle size so you get the best directions.
Bill