m248 batteries should last in the neighborhood of 6 hours on a full charge depending on the mic draw - and the condition of the battery. If it hasn't been used in a while, send it to Oade, and they may update the circuits and replace the battery ($100 or so total).
The m248 has XLR inputs, RCA outs, no XLR outs - so you will need RCA to XLR cables to run to the Mme.
Mods have been done to run it on DC, but it really isn't necessary except festival time. If you read up on the oade archive you will find that some people that have modded for DC have burned up their units beyond repair - I would not chance it unless you are an electrical engineer/real guru.
Enjoy the new toy - I love mine! (but do keep an m148 for festy season - and to have a choice)