The addition of portable GPS navigation in your vehicle is relatively inexpensive especially when compared to the overpriced dealership charge that comes when you order a factory navigation system. Some Garmin portable GPS units have built-in batteries that allow you to navigate without needing an external power source. The Garmin Nuvi 350 Personal Travel Assistant is very adaptable and includes a lithium-ion battery that you can recharge and it will remain charged for up to 8 hours. In some units, maps are loaded onto a DVD which is inserted into the system. New updated DVDs can be purchased in order to update yourself with the growth of your area.