^^ I have, but it has been awhile. I have an original, later model MixPre (not -D) and did a rundown test using fresh Duracell AA's with a pair of AKG 414 XLS's using full 48v phantom. Got to about 2 hours, 10 minutes and then the power dropped off rapidly; like within a minute or two it was unusable. Don't have their specs handy but the 414's are LD's and I believe fall fairly close to the middle in terms of current draw (~5 mA; max supported for phantom is ~10mA). Expect to get longer times from more efficient mics and shorter with less efficient mics, and longer times in general if you don't use full 48v. Don't know for sure, but Sound Devices may have also tweaked the -D version to get longer runtimes from the batteries. YMMV.