I have a Garman EMap and have been very happy with it so far. I have a DC apapter that plugs into the cigarette lighter on my boat or in my car. I bought the Garmen "Topo" software that has a combination of the entire US land map with lakes identified and some marine navigation. The only thing mine doesn't have is the tides built into it. The top of the line Garman 76 unit with a built in map is a better unit for marine;i.e. it is waterproof but also a bit more expensive. I really like having a map visual aid to give me a point of reference next to an island, especially on the water. Even with the adapter, you need to have fresh batteries in it or it will not work (2 AA's).