When I started this thread, all I was looking for was a source for a
battery for my Discus fin box. My backup battery under my panel is
about to be switched to a dedicated source to my new transponder and I
like the idea of having a separate source for my main panel instruments
and radio just in case. I lost my main battery in a glider some years
ago when a wire joint failed at the faston tab at the battery, so I
believe that a backup source is common sense.

I was considering using a 14 V seven-stack of D+ del cells for my tail
fin to take account of the extra voltage drop in the longer wiring to
the fin but decided it wasn't worth the hassle when I calculated 12 V
would work fine for the hour or two I might need it.

In any case, I hadn't intended starting rival polemics about 12 V
versus 14 V systems!

Having said that, some of the arguments for 14 V sources don't seem to
make much sense. One main argument seems to be that the higher voltage
removes the need for a second backup. Presumably using this thinking
the authors have installed heavy-duty tires on their cars and removed
their spares.

The extra 20% to 30% power from a radio transmitter also makes very
little difference. If the radio quits because of low voltage, that's a
different matter, but the extra power from a working radio is
inconsequential. Most communication problems arise from either bad
antennas or defective ones. The rubber duckies on handhelds are a
particular example of this and are horribly inefficient. Some years
ago, I did tests on the 144 MHz FM amateur frequencies from a glider
and using standard commercial equipment with good antennas was able to
maintain perfect communications with 1 watt at up to a hundred miles
with line-of-sight conditions. The 120 MHz AM aircraft radios might
not be quite so good, but a couple of watts should be good enough for
50 miles or more.