I read elsewhere that the battery level meter is rather inaccurate, and I got lucky on my first taping experience not to run out of power. I decided to run some tests to see what would work best in the field. Here are my results.
Gear and Settings
Microphones
Beyerdynamic mc930; published power consumption 4.6 mA
FR-2le
48V Phantom power: ON at startup
Mic trim: 12:00
Monitor: 10:00
Recording level: 3:00
Resolution: 16/44
CF Card: A-Data 4GB Speedy (60x)
Battery
-Internal 4xAA, alkaline: Duracell, pre-test voltage, 6.4v
Total recording time: 2:40:12
-Internal 4xAA, NiMH: Radio Shack 1800 mAh, pre-test voltage, 5.59v
Total recording time: 2:18:04
-Internal 4xAA, NiMH: Kodak 2500 mAh
Total recording time:
1st test, pre-test voltage, 5.61v: 2:57:27
2nd test, pre-test voltage, 5.37v: 2:09:35
-External, 8xAA NiMH, Radio Shack 1800 mAh
Total recording time:
1st test; pre-test voltage, 10.88 (11.19 at full charge): 4:29:17
2nd test; pre-test voltage, 11.03: 4:47:38
(*this pack will power a UA-5 for ~ 3 hours with 2 mA mics (AT835rx), ~2 hours with 6.4 mA mics (Audix M1290))
-External, 8xD alkaline, wired in series for 12v output, with 0-15v panel volt meter; deck ran until voltage dropped to ~5.75v, though I didn't start with a fresh pack. I'd estimate ~15 hours run-time with new batts**, but the shutdown voltage reading was the key piece of information in this test.
[Edit: **After some real-world field use, I have some updated results. I was able to record 32+ hours on a new set of Duracell D batteries, and the battery level meter still showed about 60% (~10 volts). Yeah. Figure in another 20-25% additional time the unit was in standby mode for sound checks, and the capacity of this simple and inexpensive pack is phenomenal. I could use these same batteries next year and they could record another whole festival. No expensive RC batts and chargers for me, thanks.]
Voltage dropped ~1.5v under load. By comparison, the UA-5 will drop voltage only ~.5v under load w/phantom engaged. The pack has a 1.1A PTC resettable fuse which never engaged. I don't know the draw of the FR-2le, but the AC adapter is marked 1A. The best news is that the battery level meter actually worked with this external pack. The FR-2le ran for several minutes after the battery icon showed totally dead. The meter usually showed half-full only minutes before shutdown with NiMH. I didn't take careful notes on the meter with the internal alkaline test.
I am still puzzled by some of these results, particularly at the difference in internal vs external powering. I tried using a plain 9v alkaline battery externally, but I didn't have a fresh one, and the ones I had wouldn't power the unit up. It seems that there needs to be a lot of juice to get it going, but is very power-efficient once powered (*see my UA-5 comment above). Best of all, for me at least, is that I now have a reliable pack for festival use and I know when to change the batteries. This isn't likely to be helpful for anyone else since 8 D cells might as well be lead.
Hopefully someone with more electronic knowledge can elaborate on these results.