There's something wrong with your setup if the 77s drain a pair of lithiums in an mp2 in 1.25 hours.
-Matt
P.S. The current draw of the mics is pretty much negligible when compared to the rest of the gear. The reason that people often have problems powering Earthworks mics is that their phantom power supplies cannot handle putting out 10 mA at 48V. My preamp is spec'd to 15 mA so I have no trouble, but the UA5 is only spec'd to 10, and I'm guessing why that device has problems with the 77s. Again, this has NOTHING to do with your run time, but everything to do with the possibility of frying your phantom power supply.