You ' re probably going to need an outside antenna if you want any decent range . We often use handheld hams between vehicles on trips , and the guys using the standard antenna from inside the vehicle can barely reach the next guy in the convoy . In general , your CB won ' t mess with your FM unless you ' re careless with the wiring . For example , if you run your antenna wire for one along the antenna wire for the other , you may pick up traces of music over CB , and every time you key the mic you ' ll get a blast of noise over FM . Easy enough to avoid , just keep the wires separate . That should be very easy with a portable . If you end up having any problem at all , it ' ll just be a little static over FM when you key the mic . If you ' re only using the CB to mess around or entertain yourself then yeah , don ' t worry about batteries . But if you plan on having it as a reliable source of communication , powering it from the car means it only works when the car is powering it . Depends what you ' re using it for .