... Battery life is almost always shorter than the manufacturer’s advertised time. You might want to purchase a spare set of batteries and use the power adapter in your RV or boat whenever possible. Make sure the GPS map can be updated with a simple download procedure. Roads and highways change all the time and the installed map will eventually become obsolete. Check the price of the download. It can be surprisingly expensive in some models. You should keep paper maps and navigation guides such as a compass to backup your GPS. Batteries can run down, or the unit might lose contact with the satellites. Having paper maps available (and knowing your current location on them) will give you peace of mind when traveling or hiking. ... Global positioning system - GPS - is a huge advance in navigation. Highly accurate map capable units can be purchased at reasonable prices and are readily available just about everywhere. The Global Positioning System is a network of satellites in different orbital paths. A GPS unit establishes contact with at least three of these satellites and uses the information received to determine altitude, longitude, and latitude. The unit takes measurements constantly and plots your path on a map (for mapping enabled GPS units), and also provides a digital display of relevant information. In order to calculate altitude, the unit must have access to at least four satellites. There are no fees or setup charges to use GPS. GPS receivers are extremely accurate due to their parallel multi-channel operation. This type of unit is quick to lock onto satellites and will hold the lock in dense foliage or city streets with tall buildings and other obstructions ...