WOW, this is one scary thread. So many WRONG answers.

Couple little tips about JR: One is that you can remove the regular battery from the slave transmitter and install a standard small 9 volt alkaline and it will work OK as a Buddy box. No need to worry about charge. Another is to beware of the fact that even if turned off the JR will indicate "ON" when the cord is plugged in. Don't let it fool you. One of these days some sue-happy person is going to collect on that one. I use JR but I respect their built-in errors.

Another item to use caution is when coupling a Hitec slave transmitter to a Futaba Master, using a Futaba old-style standard cord. The Hitec can transmit on its frequency even without a battery in it. BTDT. Remove the Hitec crystal.