|These units are small, lightweight, and portable, so you can take them virtually anywhere. They operate either on Alkaline or NiCad batteries with an average battery life of 12-24 hours of constant use. Most have 12-parallel channel receivers which lock onto satellites quickly and stay locked on in dense cover. Simple keystroke commands ease use and many are just as sophisticated as their fixed-mount counterparts. With built-in LCD displays for low power consumption and backlighting for use in bright and low-light conditions. Some units even accept an external antenna for better satellite reception.