I'm new to taping, started in the beginning of October and I do 2-3 shows a week. Most times I just go for the opening band and leave. Other times I stay for everything. All of my recordings when I've taped just the opening band are great. When I've taped opener and headliner, all the openers are great...and ALL of the headliners had battery failure in the second set! The AD-20 sucks 9v's dry and the phantom power is only slightly less greedy. For the openers, I used fresh 9v's (sometimes rechargeables, sometimes Energizers). In the beginning, I didn't change my batteries much for the headliner (wasn't aware that was the problem), but now I put a fresh 9v in for each set, though I usually have to replace the AD-20 battery late into the second set (second sets being longer than first sets).
I don't have a battery pack, primarily because I have enough crap to carry around without adding more. I've ordered a couple of dozen ultralife lithium's to use in combination with rechargeables...I don't really have a question, just wanted others to feel my pain.