RE: One Battery or Two??
I have had three TXs die in my hands over the past 10 years. I have personally witnessed another 5 or 6 do the same thing, some in flight. In that time I have not had a single RX failure, nor have I personally seen one (seen batteries unplug, switches fail, crystals crack, etc., but not a single true RX failure).
So, based on my personal experience it seems far more likely that a TX will fail than a RX. Go figure.
And don't ever think your TX is living the soft life. It gets banged around at the field, in the shop, and during transit. It is left to cook in the sun, rained on when you MUST fly, and to be dusted by other planes. It sees a fair bit of physical abuse and stress just in normal use.
On anything that I can I run two packs and two switches, since those seem to be the weakest link. If I can I eliminate the switch or use some sort of failsafe switch or something built into a regulator.
I install my RXs in as much foam as humanly possible and insulate them as best I can from vibration. I love it when I see crystals taped in to the RX tie-wrapped to the wing tube, frame, etc. Then the guy says he runs redundant RXs since they are prone to failure. Frankly I have seen very few RX failures. But I have seen a very large number of installation failures!!