Just checking in to confirm that I also have successful results running the original MixPre on 5V. I too had a USB > Hirose made by Ted and gave it a spin with my 5V/1A 4AA USB battery box using Energizer Ultimate Lithiums, here was the setup:
-4mA total mic draw (pair of DPA 4022) with P48 on
-gain knobs at 1:00
-meter brightness on lowest setting
-meter lights bouncing around 0 with peaks up to 8+
-XLR outs feeding a Tascam DR-40
-headphone turned down
I'm pretty amazed at the results. My longest test resulted in 12+ hours of runtime--I can't seem to stay awake long enough to run it down! If I ever do I'll update this thread again. I would imagine that at amplified concert levels I won't have the gain more than 9:00, and would see even longer runtime? One strange thing though--the Power light does not turn on when I have my external box connected. SD said that is the result of the MixPre being run at its voltage threshold, but that the unit is designed to shut down without damage due to insufficient voltage. Very cool!
-james