"T o d d P a t t i s t" wrote:

Of course, a 14 V battery will give you a bit more power and enable you
to run the batteries down further, but the tradeoff is usually a
cobbled-together non-standard battery stack that you can't charge with
an off-the-shelf charger.

I've run 12 volts and I've run 14 volts. The charger
comment above is the main disadvantage of 14 volts. The
secondary disadvantage is the "non-standard battery stack"
may not want to fit into your standard-sized battery
location.

An advantage to 14 volt is more radio power/longer range on
transmit. Modern radios don't cut out at lower voltage, like
older radios that assumed 13.8 volts, but they all drive the
output stages off the full voltage - the more voltage, the
more output power.

Other advantages are that you can run the battery longer
before it gets too low, and for any switchmode DC-DC
downconverters, such as I use for my IPAQ's 5 volt
requirements, you get less current draw and the battery
lasts longer (which it should since you've got more stored
energy). For me, the advantages of 14 volts outweigh the
disadvantages on my primary battery (it fits into the space
available), but not for my backup battery (the larger 14
volt battery won't fit there.)

It ultimately comes down to preference.

I agree with above.
I fly with a Dittle Radio.
If the radio is on but I do not talk, my 7AH 12V battery lasts
about 4.5 hour with the usual LNav, logger and 1530 Ipaq.
The battery will read about 11.8 volts after that time. At that
point if I make a call on the radio the chances are I will not be
heard unless I am close to the field. That is due in large part
the hand held radios seem not to do very well when it comes
to receiving a call from a radio with lower battery power. I have
made it a habit of switching to the reserve battery for my final
glide and use this battery again the next day while I charge
up the other one over night. I had an experience recently
whereby heaved in the cockpit. I tried to make a call, that I
would land in about 1/2 hour. I needed a bucket of hot water
and clean closing. I was not received as I forgot to switch the
battery. Lucky for me my call was being relayed and my wife
was ready with the goods.
Regards
Udo