ORIGINAL: Tired Old Man
I would not power a 3w ignition in any manner that was not specifically approved in their manual. You'll probably find out why eventually.
Ditto.
You might get away with sharing the receiver battery for years, but the one day when there is invisible extra noise on the 2.4 GHz band, sharing that battery could get you into a lot of trouble. I just wouldn't take the chance, even though lots of folks have been doing it successfully for a while now.
This may be common practice at some point in the future, but with the current state of 2.4 GHz technology, I wouldn't depend on it just yet. At least not until the radio manufacturers begin telling you that it is okay to share the Rx battery.
Ed Cregger