i left batteries in mine for many shows in a row and didnt see any difference in how they sounded, and i would believe what the manual says, something like ~125 hrs, but i would change them after 5 shows or so, just to be safe, you would save more money using internal power on the c1000's b/c the ps/2 you have to change after every show, it being only about ~6hrs of runtime, at least with my at4051a's