I think there have only been a small handful of failures out there so
far.

If the electrical system is clean and put together well, then the
chance of a failure is probably too remote to worry about.

FAI and contests allow for a gap of several minutes, so a simple switch
for dual batteries is good enough if you're worried about the battry
running out on you - or you forget to charge one.

A simple A/B setup takes care of the most obvious situation of leaving
the master switch on overnight and running a battery down. The second
one is hopefully still full.

-Tom