RE: One Battery or Two??
35% Plane to me means a $3500 investment. As Sweatpea states, ingnition craps out, deadstick, we have all the time, warbirds, pattern , heli's, etc etc etc and most of the time, with practice (heli's) you still have flying surface control and can usually land w/o incident.
However, For $50 bucks, that bad cell and subsequent uncontrollable crash could have been prevented with redundency. I also fly 2 rcvrs in anything that size or bigger. In addition to redundancy (forgot to turn one switch on my extra 7 years ago and it flew fine, just snapped a little slower) it makes routing the amperage easier without useing the new fancy power boxes.
My $$ is important to me so I spend a little extra, use quality parts etc etc.
Ed