Steve Leonard wrote, On 5/23/2013 11:28 AM:
My favorite quote about a backup system, and maybe it was just how I
chose to read it, was from A.J. Smith. Talking about the AS-W12 and
the addition of a second drag chute, in case there was an issue with
the primary. He said "That way, you get TWO failures per flight."

AJ isn't around to ask about it, but you why don't ask a skydiver about
why they bother with a reserve parachute ;^)

My point is, there are several reasons to have more than one battery,
and none of them are related to how much voltage a "modern" radio needs.

For your setup, with a TX 720, 14 volts may be a good choice, as it's
voltage input is specified at 13.75 volts. It was not designed to the
same requirements that have been in effect for certified radios for over
20 years, which require operation over a wide voltage range.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)
- "Transponders in Sailplanes - Feb/2010" also ADS-B, PCAS, Flarm
http://tinyurl.com/yb3xywl