yes, a weak battery can cause overload, one of my first mistakes ever taping, and also, yes, your battery could be dead early if you leave your mics plugged in, it seems to continue to draw power, despite not recording anything. So, for my one year plus 9v battery life for dpa 4061's, I plug the mics into the battery box only just a couple minutes before recording and I unplug them at the end of the night (not usually between bands or sets, though). If your std battery box works with the dpa's, I'd use it almost exclusively over the preamp, just my opinion, of course, but recording bands like Melvins, Mike Watt and Dinosaur Jr, I haven't had a brickwalling issue, even when recording right near the drums or the stacks
sooooooooo, use the sp battery box with a decent 9v and your dpa's, should be good for all loud shows, for certain!