Well the 4 D-cell external battery pack didn't work out the way I had hoped.
Test specifics..
--Batteries - Duracell Procell (about 15,000 mah)
--Starting voltage - 3.22VDC fed to unit via the DC-in jack
--Ran recorder for 12 1/2 hrs with display on the brightest setting, with the record button lit, recording at 24/48 with the gain @ 40-- Voltage dropped to 2.77vdc
--Paused test for 10 hrs
-- battery pack now at 2.9 R09hr would not power up. Put the internals in, turned unit on, plugged in the external, then removed the internals and the unit stayed on
-- recorder ran for another 8+ hours, then shut off leaving the last file corrupt
--voltage was at 2.7vdc when unit shut down
So a total of about 20 hrs. I'm thinking if I make some dummy battery slugs and feed the voltage directly into the battery compartment it would have gone much longer and the battery meter would have functioned as well. At 30,000 mah capacity, I would think this pack should then run the R09hr for at least 60 hrs.
One thing I noted that was good; with batteries in the unit, you could unplug the external power and it would seamlessly switch back and forth. As long as you have a good voltage at either source, you could hot-swap the other source.