2-12 volt, 12 amp hour batteries wired in series nets how many amp hours at 24 volts?

Still 12 ah.  The number of watts is doubled though. Watts are the measure of work.

wired in series, you get 24V at 12AH.
wired in parallel, you get 12V at 24AH.

ar-jedi

VxA=W in dc. 288W either way.

i don't understand how 288W comes into play here.  i think you mean 288WH.  
this is just one capacity, though, on the capacity curve –– which is dependent on load.

ar-jedi

12x24=288 2ea 12Ah battery at 12v.  Yes I should have put Wh instead of W. People get all wrapped up in volts or amps. It is Watts that do the work.

right, but the OP is asking about capacity.  

you can get a lot more than 288W out of a pair of 12V 12AH batteries.  
you just can't do so for long.

ar-jedi

I bought my RBC-6 here:

http://www.gruberpower.com/gruberpower/advertising/Batteries/default.asp

Two other considerations besides battery capacity.  

(1)  Weight.  How much can you carry?  How much do you really want to carry?

(2)  Shape.  You may be able to find, there at Gruber, shapes/dimensions that will better fit with your needs.

In a real "emergency" situation you will not be operating your radio like contesting.  You won't even operate it like a net control.  You will listen a lot and transmit as little as possible, so take that into your power calculations.  And you will only get about half the amp-hour capacity of what the batteries are rated.

Looking at the 12 AH batteries, I think that is a lot more capacity than what your PRC-320's batteries were rated, correct?  So they should give good performance for your radio.

I have 2 RBC-6 sets... that is, four 12 v 12 AH gel cell batteries.  The Battery Tender 800 (equiv to the Battery Tender Jr) easily keeps all four topped off.