Its risk/reward right? We are in warbird forum, warbirds usually benefit from nose weight so toting battery capacity around instead of lead is a no brainer.
3D guys feel the lighter weight is worth the risk of a single battery. Based on my experience with single battery setups, which is fairly extensive compared to Joe Sunday flyer, I'll assume that risk for what I feel is a benefit.
My point was, and I'm sure you follow, is anything can fail in one of these models. Planes with single elevator servos are at a greater risk than a setup with split elevators, same with ailerons, batteries, whatever.
Bottom line is I'm not implying a single battery is a more reliable or better setup, just that, properly setup with decent quality equipment, its not the doom and gloom setup that some folks imply.