I run a Littlebox with M1290s. Here's a sample (but with CA11 omnis mixed in for a little more oomph in the low end).
http://www.archive.org/details/rre2011-01-28.m1290hc.flac16fI usually run matrices since I got my DR2D but have a few straight M1290 to LB that aren't on archive, can post them if you're interested.
I have the dual 9V version. For a long time, I was getting 4.5 hrs per pair of 9V. Then my LB had some problems and I sent it in to Jon and I'm pretty sure he just sent me a new one. The one time I tested battery life on the new one, it was more like 7 hrs - but just to make it even less scientific that was with Energizers, previously used Duracells.
As to the low voltage setting, I've never had the guts to run it at a show but around the house, I don't hear a difference between high and low voltage. Perhaps it wold be a different story at higher SPLs, but not sure why. Interestingly, I asked Cliff Castle at Audix about powering and he sqid they definitely needed 44+ V or they'd be noisy, that was not my experience, if there's any more noise it's pretty subtle.
Here's a sample of pure AUD: Audix Micro M1290 (cards, DIN, 6' high, ~70' back, outdoors) > Littlebox > DR2D.
http://homepage.mac.com/satterwill/halfwaybacks2010-05-29t07.flacFor comparison purposes, AKG C414EB > MR-1000 from a few rows closer:
http://www.archive.org/details/waybacks2010-05-29.waybacks2010-05-29.lehman.aif