It is probably most easiest to just hook it up directly to the battery. When you put your Zumo in it's mount...it's on. What most are missing is that (at least in my case anyway) I do not use my Zumo except for when I may go on a trip. If I'm not on a trip, the Zumo isn't with me. And even when on a trip it is only on the bike when I'm traveling, when I'm in for for the night of I'm not on the bike for awhile (eating a meal for instance) my Zumo comes off of the mount and is locked away. I do not worry about running my battery down when using my GPS.
Dennis