Most of the FAI guys in the Uk are using a single 4300 5 cell battery with two leads into two switches these days, even if one cell goes down you still will have a 4 cell battery as long as its not shorted out, as someone said our batteries and switches now days are far more reliable than they used to be, just use heavy duty wire and switches, incidently in over 40 years of flying RC I have never (yet) had either a servo or switch fail in flight, had them but always noticed on the ground or during maintenance which I do a lot of.

Mike