If I put two new fresh Duracell (regular or Ultras) in an Edirol R-09HR and do "Line In" recording from another source (DAT or memory card) and assuming I put it on "power save", approximately how long will these 2 batteries last? I'm trying to see what will occur with some long shows that I have in Oct-Nov. These shows range from 4 - 7 hours. Thanks!!