RE: rx battery
The uninitiated might make a bad assumption on the above discussion of Zenner Diodes. You must use a dropping resistor or load in front of the zenner which can cause a lot of excess heating if the difference between the source voltage and regulated load is large; in short, you can not just put a zenner diode in parallel with the load to drop the voltage. This becomes even more complicated if there is a large variance in the load current during normal operation.