RE: Cons for installing redundant receiver batteries ?
John, I used to do what you did, use two batteries isolated via diodes etc. Worked well. However, when I got really serious about power supplies, BVM F4, AMT Pegasus arrived 14v years ago, , (and its still around !) it was Tony Fradiowack, then working in NASA's model dept who suggested I just connect two Duralites straight onto the RX bus. This I did, still do, but being a nerd I wanted to test it for myself. Never did I find a battery that discharged into the other at any significant rate, with or without regulators and I tried flat batteries and some which were completely dead, wouldn't even take any charge. That is the conclusion on the NOBS battery site too where the author is a battery expert from the industrial field(GE). Its worth a read. I also thought it logical to connect the two batteries to opposite ends of the bus, turned out that doubles the current capability of the bus. Can't hurt even if there is no real practical advantage.
I agree that a standby battery in a tx would be of benefit but after gathering a LOT of data via my Weatronics systems , I can see that tx batteries have a very easy life compared with those in the Rx. If one produces a graph on Weatronics software of Tx batt voltage its almost a straight line with a gentle decline indicating a near constant small current. On the other hand the current (the voltage stays very stable) in the rx primary battery shows considerable fluctuation, varying between 3 amps with spikes upto 10 amps on an AirWorld Hawk. Do these variations increase the risk of battery failure, I don' t know but its very reassurring to have TWO battery circuits EACH independently capable of running the system.
I think it was David Searles who published the fact that JPO found that the MAIN cause of crashes in jet models was battery failure, dual batteries will virtually eliminate that risk. Its easy to do so why not do it ?
We cannot remove ALL risk in aviation, a 747 has only one fin, one came off in Japan, years ago, but they still fly with one fin, but at least we can go a long way to improve safety by eliminating obvious and serious risk, particularly when the solution is easy and cheap. A failure of a single battery and its all over, with a dual battery installation failure of a single battery is a non event.
and may I ask why Xairflier changes his batteries every year, worried about failure perhaps ? Some of my batteries in Dual installations are years old, I will change them only when they start to show a deterioration in service , confident that the risk of a dual simultaneous failure is negligible.