It is preferable to have a device that can be supported with external power, like a travel charger or a cigarette lighter power cable to recharge or at least extend the life of the batteries in your GPS units. Due to the power requirements while in use, the device should support standard batteries (AA or AAA) that you can carry in your pocket or pack for easy replacement on the trail. Lithium batteries are often recommended for the newer GPS devices to ensure longer battery life, and power geocachers or avid GPS enthusiasts should consider rechargeable batteries. You sure don’t want to end up lost because your GPS unit’s battery died on you while you were out in the middle of nowhere, so planning ahead is always smart. Stay safe and have fun!